SlideShare una empresa de Scribd logo
1 de 79
Descargar para leer sin conexión
Introduction to Monte Carlo in Finance
Giovanni Della Lunga
WORKSHOP IN QUANTITATIVE FINANCE
Bologna - May 12-13, 2016
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 1 / 79
Valuation of American Option
Outline
1 Valuation of American Option
2 The Hull and White Model
3 MCS for CVA Estimation
Definitions
CVA of a Plain Vanilla Swap: the Analytical Model
CVA of a Plain Vanilla Swap: the Simulation Approach
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 2 / 79
Valuation of American Option
Valuation of American Option by Simulation
As we have seen Monte Carlo simulation is a flexible and powerful
numerical method to value financial derivatives of any kind.
However being a forward evolving technique, it is per se not suited to
address the valuation of American or Bermudan options which are
valued in general by backwards induction.
Longstaff and Schwartz provide a numerically efficient method to
resolve this problem by what they call Least-Squares Monte Carlo.
The problem with Monte Carlo is that the decision to exercise an
American option or not is dependent on the continuation value.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 3 / 79
Valuation of American Option
Valuation of American Option by Simulation
Consider a simulation with M + 1 points in time and I paths.
Given a simulated index level St,i , t ∈ {0, ..., T}, i ∈ {1, ..., I}, what is
the continuation value Ct,i (St,i ), i.e. the expected payoff of not
exercising the option?
The approach of Longstaff-Schwartz approximates continuation values
for American options in the backwards steps by an ordinary
least-squares regression.
Equipped with such approximations, the option is exercised if the
approximate continuation value is lower than the value of immediate
exercise. Otherwise it is not exercised.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 4 / 79
Valuation of American Option
Valuation of American Option by Simulation
In order to explain the metodology, let’s start from a simpler problem.
Consider a bermudan option which is similar to an american option,
except that it can be early exercised once only on a specific set of
dates.
In the next figure, we can represent the schedule of a put bermudan
option with strike K and maturity in 6 years. Each year you can
choose whether to exercise or not ...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 5 / 79
Valuation of American Option
Valuation of American Option by Simulation
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 6 / 79
Valuation of American Option
Valuation of American Option by Simulation
Let’s consider a simpler example: a put option which can be exercised
early only once ...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 7 / 79
Valuation of American Option
Valuation of American Option by Simulation
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 8 / 79
Valuation of American Option
Valuation of American Option by Simulation
Can we price this product by means of a Monte Carlo? Yes we can!
Let’s see how.
Let’s implement a MC which actually simulates, besides the evolution
of the market, what an investor holding this option would do (clearly
an investor who lives in the risk neutral world). In the following
example we will assume the following data, S(T) =, K =, r =, σ =,
t1 = 1y, T = 2y.
We simulate that 1y has passed, computing the new value of the
asset and the new value of the money market account
S(t1 = 1y) = S(t0)e(r−1
2
σ2)(t1−t0)+σ
√
t1−t0N(0,1)
B(t1 = 1y) = B(t0)er(t1−t0)
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 9 / 79
Valuation of American Option
Valuation of American Option by Simulation
At this point the investor could exercise. How does he know if it is
convenient?
In case of exercise he knows exactly the payoff he’s getting.
In case he continues, he knows that it is the same of having a
European Put Option.
So, in mathematical terms we have the following payoff in t1
max [K − S(t1), P(t1, T; S(t1), K)]
where P(t1, T; S(t1), K) is the price of a Put which we compute
analytically! In the jargon of american products, P is called the
continuation value, i.e. the value of holding the option instead of
early exercising it.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 10 / 79
Valuation of American Option
Valuation of American Option by Simulation
So the premium of the option is the average of this discounted payoff
calculated in each iteration of the Monte Carlo procedure.
1
N
i
max [K − Si (t1), P(t1, T; Si (t1), K)]
Some considerations are in order.
We could have priced this product because we have an analytical
pricing formula for the put. What if we didn’t have it?
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 11 / 79
Valuation of American Option
Valuation of American Option by Simulation
Brute force solution: for each realization of S(t1) we run another
Monte Carlo to price the put.
This method (called Nested Monte Carlo) is very time consuming.
For this very simple case it’s time of execution grows as N2, which
becomes prohibitive when you deal with more than one exercise date!
Let’s search for a finer solution analyzing the relationship between the
continuation value (in this very simple example) and the simulated
realization of S at step t1.
let’s plot the discounted payoff at maturity, Pi , versus Si (t1) ...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 12 / 79
Valuation of American Option
Valuation of American Option by Simulation
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 13 / 79
Valuation of American Option
Valuation of American Option by Simulation
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 14 / 79
Valuation of American Option
As you can see, the analytical price of the put is a curve which kinds
of interpolate the cloud of Monte Carlo points.
This suggest us that the price at time t1 can be computed by means
of an average on all discounted payoff (i.e. the barycentre of the
cloud made of discounted payoff)
So maybe... the future value of an option can be seen as the problem
of finding the curve that best fits the cloud of discounted payoff (up
to date of interest)!!!
In the next slide, for example, there is a curve found by means of a
linear regression on a polynomial of 5th order...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 15 / 79
Valuation of American Option
Valuation of American Option by Simulation
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 16 / 79
Valuation of American Option
Valuation of American Option by Simulation
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 17 / 79
Valuation of American Option
Valuation of American Option by Simulation
We now have an empirical pricing formula for the put to be used in
my MCS
P(t1, T, S(t1), K) = c0 + c1S(t1) + c2S(t1)2
+ c3S(t1)3
+ c4S(t1)4
+ c5S(t1)5
The formula is obviously fast, the cost of the algorithm being the best
fit.
Please note that we could have used any form for the curve (not only
a plynomial).
This method has the advantage that it can be solved as a linear
regression, which is fast.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 18 / 79
Valuation of American Option
The Longstaff-Schwartz Algorithm
The major insight of Longstaff-Schwartz is to estimate the
continuation value Ct,i by ordinary least-squares regression, therefore
the name ”Least Square Monte Carlo” for their algorithm;
They propose to regress the I continuation values Yt,i against the I
simulated index levels St,i .
Given D basis functions b with b1, . . . , bD : RD → R for the
regression, the continuation value Ct,i is according to their approach
approximated by:
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 19 / 79
Valuation of American Option
The Longstaff-Schwartz Algorithm
Given D basis functions b with b1, . . . , bD : RD → R for the
regression, the continuation value Ct,i is according to their approach
approximated by:
ˆCt,i =
D
d=1
αd,tbd (St,i ) (1)
The optimal regression parameters αd,t are the result of the
minimization
min
α1,t ,...,αD,t
1
I
I
i=1
Yt,i −
D
d=1
αd,tbd (St,i )
2
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 20 / 79
Valuation of American Option
The Longstaff-Schwartz Algorithm
Simulate I index level paths with M + 1 points in time leading to
index level values St,i , t ∈ {0, ..., T}, i ∈ {1, ..., I};
For t = T the option value is VT,i = hT (ST,i ) by arbitrage
Start iterating backwards t = T − ∆t, . . . , ∆t:
regress the Tt,i against the St,i , i ∈ {1, . . . , I}, given D basis function b
approximate Ct,i by ˆCt,i according to (1) given the optimal parameters
αd,t from (2)
set
Vt,i =
ht(St,i ) if ht(St,i ) > ˆCt,i exercise takes place
Yt,i if ht(St,i ) ≤ ˆCt,i no exercise takes place
repeat iteration steps until t = ∆t;
for t = 0 calculate the LSM estimator
ˆV LSM
0 = e−r∆t 1
I
I
i=1
V∆t,i
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 21 / 79
Valuation of American Option
Notebook
GitHub : polyhedron-gdl;
Notebook : mcs american;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 22 / 79
The Hull and White Model
Outline
1 Valuation of American Option
2 The Hull and White Model
3 MCS for CVA Estimation
Definitions
CVA of a Plain Vanilla Swap: the Analytical Model
CVA of a Plain Vanilla Swap: the Simulation Approach
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 23 / 79
The Hull and White Model
Hull-White Model
Described by the SDE for the short rate
dr = (θ(t) − ar)dt + σdw (1)
See Brigo-Mercurio ...
Our version simplified: a and σ constant;
AKA Extended Vasicek (Note: r(t) is Gaussian);
θ determined uniquely by term structure;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 24 / 79
The Hull and White Model
Hull-White Model: Solving for r(t)
d(eat
r) = eat
dr + aeat
rdt = θ(t)eat
+ eat
σdw
integrating both sides we obtain
eat
r(t) = r(0) +
t
0
θ(s)eas
ds + σ
t
0
eas
dw(s)
simplify
r(t) = r(0)e−at
+
t
0
θ(s)e−a(t−s)
ds + σ
t
0
e−a(t−s)
dw(s)
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 25 / 79
The Hull and White Model
Hull-White Model: Solving for P(t,T)
P(t, T) = V (t, r(t)) where V solves the PDE
Vt + (θ(t) − ar)Vr +
1
2
σ2
Vrr − rV = 0
Final-time condition V (T, r) = 1 for all r at t = T;
Ansatz:
V = A(t, T)e−B(t,T)r(t)
A and B must satisfy:
At − θ(t)AB +
1
2
σ2
(AB)2
= 0, and Bt − aB + 1 = 0
Final-time conditions
A(T, T) = 1 and B(T, T) = 0
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 26 / 79
The Hull and White Model
Hull-White Model: Solving for P(t,T)
B independent of θ so
B(t, T) =
1
a
1 − e−a(T−t)
(2)
Solving for A requires integration of θ
A(t, T) = exp

−
T
t
θ(s)B(s, T)ds −
σ2
2a2
(B(t, T) − T + t) −
σ2
4a
B(t, T)2


Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 27 / 79
The Hull and White Model
Hull-White Model: Determining θ
Determining θ from the term structure at time 0;
Goal: demonstrate the relation
θ(t) =
∂f
f ∂T
(0, t) + af (0, t) +
σ2
2a
(1 − e−2at
) (3)
Recall
f (t, T) = −∂ log P(t, T)/∂T
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 28 / 79
The Hull and White Model
Hull-White Model: Determining θ
We have
− log P(0, T) =
T
0
θ(s)B(s, T)ds +
σ2
2a2
[B(0, T) − T] +
σ2
4a
B(0, T)2
+ B(0, T)r0
Differentiating and using that B(T, T) = 1 and ∂T B − 1 = −aB we
get
f (0, T) =
T
0
θ(s)∂T B(s, T)ds−
σ2
2a2
B(0, T)+
σ2
2a2
B(0, T)∂T B(0, T)+∂T B(0, T)r0
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 29 / 79
The Hull and White Model
Hull-White Model: Determining θ
Differentiating again, get:
∂T f (0, T) = θ(T) +
T
0
θ(s)∂TT B(s, T)ds
−
σ2
2a2
∂T B(0, T)
+
σ2
2a2
[(∂T B(0, T))2
+ B(0, T)∂TT B(0, T)]
+ ∂TT B(0, T)r0
(4)
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 30 / 79
The Hull and White Model
Hull-White Model: Determining θ
Combine these equations, and use a∂T B + ∂TT B = 0;
Get:
af (0, T) + ∂T f (0, T) = θ(T) −
σ2
2a
(aB + ∂T B) +
σ2
2a
[aB∂T B + (∂T B)2
+ B∂TT B]
Substitute formula for B and simplify to get
af (0, T) + ∂T f (0, T) = θ(T) −
σ2
2a
(1 − e−2aT
)
QED
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 31 / 79
The Hull and White Model
Additive Factor Gaussian Model
The model is given by dynamics (Brigo-Mercurio p. 143):
r(t) = x(t) + φ(t)
where
dx(t) = −ax(t)dt + σdWt x(0) = 0
and φ is a deterministic shift which is added in order to fit exactly the
initial zero coupon curve
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 32 / 79
The Hull and White Model
Additive Factor Gaussian Model
So the short rate r(t) is distributed normally with mean and variance
given by (Brigo-Mercurio p.144 equations 4.6 with η = 0)
E(rt|rs) = x(s)e−a(t−s)
+ φ(t)
Var(rt|rs) =
σ2
2a
1 − e−2a(t−s)
where φ(T) = f M(0, T) + σ2
2a 1 − e−aT 2
and f M(0, T) is the
market instantaneous forward rate at time t as seen at time 0.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 33 / 79
The Hull and White Model
Additive Factor Gaussian Model
Model discount factors are calculated as in Brigo-Mercurio (section
4.2):
P(t, T) =
PM(0, T)
PM(0, t)
exp (A(t, T))
A(t, T) =
1
2
[V (t, T) − V (0, T) + V (0, t)] −
1 − e−a(T−t)
a
x(t)
where
V (t, T) =
σ2
a2
T − t +
2
a
e−a(T−t)
−
1
2a
e−2a(T−t)
−
3
2a
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 34 / 79
MCS for CVA Estimation
Outline
1 Valuation of American Option
2 The Hull and White Model
3 MCS for CVA Estimation
Definitions
CVA of a Plain Vanilla Swap: the Analytical Model
CVA of a Plain Vanilla Swap: the Simulation Approach
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 35 / 79
MCS for CVA Estimation Definitions
Counterparty Risk
In general a given company, say a financial institution A, will have
portfolios with many other counterparties, varying among sovereign
entities, corporates, hedge funds, insurance companies;
Counterparty credit exposure is the amount a company, say A, could
potentially lose in the event of one of its counterparties defaulting.
As we’ll see in more details, it can be computed by simulating in
different scenarios and at different times in the future, the price of the
transactions with the given counterparty, and then by using some
chosen statistic to characterise the price distributions that have been
generated.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 36 / 79
MCS for CVA Estimation Definitions
CVA Context
Counterparty risk can be considered broadly from two different points
of view;
The first point of view is risk management, leading to capital
requirements revision, trading limits discussions and so on;
The second point of view is valuation or pricing, leading to amounts
called Credit Valuation Adjustment (CVA) and extensions thereof,
including netting, collateral, re-hypothecation, close-out specification,
wrong way risk and funding cost;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 37 / 79
MCS for CVA Estimation Definitions
Example: CVA of plain vanilla Interest-Rate Swap
Consider counterparties A and B who enter into an interest-rate swap
where A receives every six months the 6-month Libor rate on a
notional of 100 million euro, while paying to B a fixed amount equal
to the par 10-year swap rate on the same notional observed at
inception.
This is a typical swap contract with value zero at inception.
As time passes and market conditions change, the value of the swap
changes accordingly. Thus, if the swap rate decreases (resp.
increases), the transaction will be out of the money (resp. in the
money) as seen from A’s point of view.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 38 / 79
MCS for CVA Estimation Definitions
Example: CVA of plain vanilla Interest-Rate Swap
Therefore, if B were to default at a point in the life of the trade when
swap rates had increased, then A would need to replace in the
market—at higher cost than the fixed amount being paid to B—the
floating cashflows promised and not delivered by B.
To compute the credit exposure for the swap, we would need to
estimate the values the swap could take in different market scenarios
at points in the future.
For practical reason it can be useful to characterise the distribution of
values with some quantity which can be useful for various risk
controlling;
For example we could compute the so called Expected Positive
Exposure (more in the following) as
EPEt = E[V +
t ]
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 39 / 79
MCS for CVA Estimation Definitions
Exposure Profile: EPE
Figure shows the EPE of the swap price distribution, over its entire
life, as seen from party A’s point of view.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 40 / 79
MCS for CVA Estimation Definitions
Exposure Profile: Value Density
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 41 / 79
MCS for CVA Estimation Definitions
Exposure Profile
Figure shows the full price
distribution over time.
The fair value for the swap, and
this must therefore have value
(and hence exposure level)
identically equal to zero at
inception.
Similarly, towards the end of the
transaction, when all payments
but one due under the swap
have been paid, the exposure
remaining is that from only a
single coupon exchange.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 42 / 79
MCS for CVA Estimation Definitions
Exposure Profile
This explains what happens at the
right end of the profile.
At intermediate times, the shape of
the profile is the result of opposing
effects.
On the one hand, as the interest rates
underlying the swap diffuse, there is
more variability in the realised Libor
rates, potentially leading to higher
exposure.
On the other hand, as time evolves
there are fewer payments remaining
under the swap, and this mitigates the
effect of diffusing rates.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 43 / 79
MCS for CVA Estimation Definitions
Exposure Profiles
So there are two main effects that determine the credit exposure over
time for a single transaction or for a portfolio of transactions with the
same counterparty: diffusion and amortization;
as time passes, the ”diffusion effect” tends to increase the exposure,
since there is greater variability and, hence, greater potential for
market price factors to move significantly away fro current levels;
the ”amortization effect”, in contrast, tends to decrease the exposure
over time, because it reduces the remaining cash flows that are
exposed to default;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 44 / 79
MCS for CVA Estimation Definitions
Exposure Profiles
For single cash flow products, such as FX Forwards, the potential
exposure peaks at the maturity of the transaction, because it is driven
purely by ”diffusion effect”;
on the other hand, for products with multiple cash flows, such as
interest-rate swaps, the potential exposure usually peaks at one-third
to one-half of the way into the life of the transaction;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 45 / 79
MCS for CVA Estimation Definitions
Credit Value Adjustment
Credit Value Adjustment (CVA) is by definition the difference
between the risk-free portfolio value and the true portfolio value that
takes into account the possibility of a counterparty’s default;
in other words CVA is the market value of counterparty credit risk;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 46 / 79
MCS for CVA Estimation Definitions
Credit Value Adjustment
Assuming independence between exposure and counterparty’s credit
quality greatly simplifies the analysis.
under this assumption we can write
CVA = (1 − R)
T
0
EE (t)dPD(0, t) (5)
where EE (t) is the risk-neutral discounted expected exposure (EE)
given by
EE (t) = EQ B0
Bt
E(t) (6)
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 47 / 79
MCS for CVA Estimation Definitions
Credit Value Adjustment
In general calculating discounted EE requires simulations;
Exposure is simulated at a fixed set of simulation dates, therefore the
integral in (5) has to be approximated by the sum:
CVA = (1 − R)
N
i=1
EE (tk)PD(tk−1, tk) (7)
Since expectation in (6) is risk-neutral, scenario models for all price
factors should be arbitrage free;
This is achieved by appropriate calibration of drifts and volatilities
specified in the price-factor evolution model;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 48 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
At valuation time t, and provided the counterparty has not defaulted
before t, i.e. on {τ > t}, the price of our payoff with maturity T
under counterparty risk is
Et[¯Π(t, T)] = Et[Π(t, T)] − Et[LGD It≤τ≤T D(t, τ)(NPV (τ))+
]
positive counterparty-risk adjustment
= Et[Π(t, T)] − UCVA(t, T)
(8)
with
UCVA(t, T) = Et[LGD It≤τ≤T D(t, τ)(NPV (τ))+
]
= Et[LGD It≤τ≤T D(t, τ)EAD]
(9)
Where LGD = 1 − REC is the loss given default, and the recovery
fraction REC is assumed to be deterministic.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 49 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
It is clear that the value of a defaultable claim is the sum of the value
of the corresponding default-free claim minus a positive adjustment.
The positive adjustment to be subtracted is called (Unilateral) Credit
Valuation Adjustment (CVA), and it is given by a call option (with
zero strike) on the residual NPV at default, giving nonzero
contribution only in scenario where τ ≤ T.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 50 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
Counterparty risk thus adds and optionality level to the original payoff.
This renders the counterparty risk payoff model dependent even when
the original payoff is model independent.
This implies, for example, that while the valuation of swaps without
counterparty risk is model independent, requiring no dynamical model
for the term structure (no volatility and correlations in particular), the
valuation of swaps under counterpaty risk will require and interest
rate model.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 51 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
Now we explore the well known result that the component of the IRS
price due to counterparty risk is the sum of swaption prices with
different maturities, each weighted with the probability of defaulting
around that maturity.
Let us suppose that we are a default free counterparty ”B” entering a
payer swap with a defaultable counterparty ”C”, exchanging fixed for
floating payments at times Ta+1, . . . , Tb.
Denote by βi the year fraction between Ti−1 and Ti , and by P(t, Ti )
the default-free zero coupon bond price at time t for maturity Ti . We
take a unit notional on the swap.
The contract requires us to pay a fixed rate K and to receive the
floating rate L resetting one period earlier until the default time τ of
”B” or until final maturity T if τ > T.
The fair forward-swap rate K at a given time t in a default-free
market is the one which renders the swap zero-valued in t.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 52 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
In the risk-free case the discounted payoff for a payer IRS is
b
i=a+1
D(t, Ti )βi (L(Ti−1, Ti ) − K) (10)
and the forward swap rate rendering the contract fair is
K = S(t; Ta, Tb) = Sa,b(t) =
P(t, Ta) − P(t, Tb)
b
i=a+1
P(t, Ti )βi
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 53 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
Of course if we consider the possibility that ”C” may default, the
correct spread to be paid in the fixed leg is lower as we are willing to
be rewarded for bearing this default risk.
In particular we have
UCVA(t, Tb) = LGD Et[Iτ≤Tb
D(t, τ)(NPV (τ))+
]
= LGD
Tb
Ta
PS (t; s, Tb, K, S(t; s, Tb), σs,Tb
) dsQ{τ ≤ s}
(11)
being PS (t; s, Tb, K, S(t; s, Tb), σs,Tb
) the price in t of a swaption
with maturity s, strike K underlying forward swap rate S(t; s, Tb),
volatility σs,Tb
and underlying swap with final maturity Tb.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 54 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
The proof is the following: given independence between τ and the
interest rates, and given that the residual NPV is a forward start IRS
starting at the default time, the option on the residual NPV is a sum
of swaptions with maturities ranging the possible values of the default
time, each weighted (thanks to the independence assumption) by the
probabilities of defaulting around each time value.
We can simplify formulas allow the default to happen only at points
Ti of the fixed leg payment grid.
In this way the expected loss part is simplified.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 55 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
The General Unilateral Counterparty Risk Pricing Formula
Indeed in the case of postponed (default occour to the first Ti
following τ) payoff we obtain:
UCVA(t, Tb) = LGD Et [Iτ≤Tb
D(t, τ)(NPV (τ))+
]
= LGD
b−1
i=a+1
PS (t; s, Tb, K, S(t; s, Tb), σs,Tb ) (Q{τ ≥ Ti } − Q{τ > Ti })
(12)
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 56 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model
Notebook
GitHub : polyhedron-gdl;
Notebook : n09 cva swap;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 57 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Monte Carlo Framework for CVA
The industry practice to compute exposure is to use a simple Monte Carlo
framework implemented in three steps:
1 scenario generation,
2 pricing
3 aggregation.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 58 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Monte Carlo Framework for CVA
The first step involves generating scenarios of the underlying risk
factors at future points in time.
Simple products can then be priced on each scenario and each time
step, therefore generating empirical price distributions.
From the price distribution at each time it is then possible to extract
convenient statistical quantities.
Exposure of portfolios can be computed by consistently pricing
different products on the same underlying scenarios and aggregating
the results taking into account possible netting and collateral
agreement with the counterparty.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 59 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Monte Carlo Framework for CVA
If taken literally, this approach works only for relatively simple
products which can be priced analytically, or which can be
approximated in analytical form, and which do not need complex
calibrations depending on market scenarios.
More exotic products requiring relatively complex pricing, cannot be
treated in this way.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 60 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
CVA of a Plain Vanilla Swap: the Simulation Approach
1 Simulate yield curve at future dates
2 Calculate your derivatives portfolio NPV (net present value) at each
time point for each scenario
3 Calculate CVA as sum of Expected Exposure multiplied by probability
of default at this interval
CVA = (1 − R) DF(t)EE(t)dQt
where R is the Recovery Rate (normally set to 40%) EE(t) is the
expected exposure at time t and dQt the survival probability density,
DF(t) is the discount factor at time t.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 61 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
CVA of a Plain Vanilla Swap: the Simulation Approach
In this simple example we will use a modified version of Hull White
model to generate future yield curves. In practice many banks use
some yield curve evolution models based on this model.
For each point of time we will generate whole yield curve based on
short rate. Then we will price our interest rate swap on each of these
curves;
To approximate CVA we will use BASEL III formula for regulatory
capital charge approximating default probability [or survival
probability ] as exp(−ST /(1 − R)) so we get
CVA = (1 − R)
i
EE(Ti ) + EE(Ti−1
2
e−S(Ti−1)/(1−R)
− e−S(Ti )/(1−R)
where EE is the discounted Expected Exposure of portfolio.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 62 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
CVA of a Plain Vanilla Swap: the Simulation Approach
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 63 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Notebook
GitHub : polyhedron-gdl;
Notebook :
n10 mcs cva swap;
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 64 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Implementation Challenges
The Monte Carlo framework we have shown in the previous section,
seems to give a good implementation recipe.
For a given portfolio of transactions we could identify the underlying
risk factors and simulate forward (or spot) prices, taking into account
correlations if required, use functions already implemented to price
each product, and then derive statistical quantities.
As we have mentioned already, this could be the approach followed by
a financial institution to assess the counterparty credit risk of its OTC
derivatives portfolios.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 65 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Implementation Challenges
In the implementation phase, however, there can be issues which need
to be addressed.
The generation of correlated scenarios is not trivial, as there can be
thousands of different risk factors driving the dynamics of products in
the portfolio.
Consider for example an equity portfolio, where each underlying stock
needs, at least in principle, a specific simulation.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 66 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Implementation Challenges
Not all products can be computed in analytical form.
Most exotics are priced on grids using PDEs or using Monte Carlo
approaches.
In these cases the exposure computation would require a Monte Carlo
simulation for scenarios and a Monte Carlo simulation, or a PDE
computation, for each scenario and time step to price the instrument.
This becomes quickly unfeasible from a computational point of view.
In addition, depending on the model used for pricing, calibration could
also become problematic, as it has to be performed at each scenario.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 67 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
American Monte Carlo
The points highlighted in the previous section clearly show that the
classical Monte Carlo scheme has intrinsic limitations and that we
need an alternative approach.
There are possibilities to circumvent in a systematic way some of the
problems related to valuation and architecture.
The basic idea is to approach the counterparty exposure problem as a
pricing problem, and thus to use pricing algorithms, which generate
not just the value of a trade at inception, but rather a price
distribution at predetermined time steps.
One possibility is to use the so called American Monte Carlo
algorithm, which we will refer to as, simply, the AMC algorithm.
The main feature of this algorithm is that, instead of building a price
moving forward in time, it starts from maturity, where the value of
the transaction is known, and goes backwards, till the inception.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 68 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Let’s illustrate with a Bermuda Swaption which can be exercised at 2 dates, T1
and T2.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 69 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Forward Phase: we diffuse risk factors and store in memory contract cash flows
and payoff variables as the will be used in the Backward Phase.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 70 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Backward Phase: we discount payoff contract and add cash flows up to T2.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 71 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Backward Phase: At T2 we obtain a cloud of points...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 72 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
... regression is performed to obtain product fair value at T2 as a function of
regression basis.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 73 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
We discount to T1 obtaining a cloud of points (adding present cash flow from
forward phase).
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 74 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Regression is performed at T1 as a function of regression basis.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 75 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Forward Phase: we then move forward again and invoke regression functions with
the new set of MC paths ...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 76 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
We can compute distribution of MTMs, exposure, EPE, PFE, etc...
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 77 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
AMC CVA Simulation
Recap
Important Remark: In Phase 3, MC diffusion can be different from
Phase 1.
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 78 / 79
MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach
Credits
Damiano Brigo, Fabio Mercurio ”Interest Rate Models — Theory and
Practice” Springer Finance (2006)
Damiano Brigo, Massimo Morini, Andrea Pallavicini ”Counterparty
Credit Risk, Collateral and Funding” Wiley Finance (2013)
Umberto Cherubini, Elisa Luciano, Walter Vecchiato ”Copula
Methods in Finance” Wiley Finance (2004)
Tommaso Gabbriellini ”American Options with Monte Carlo”
Presentation on Slideshare
Yves Hilpisch ”Derivatives Analytics with Python” Wiley Finance
(2015)
Don L. McLeish ”Monte Carlo Simulation and Finance” Wiley
Finance (2005)
Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 79 / 79

Más contenido relacionado

La actualidad más candente

Chapter 18 internal ratings based approach
Chapter 18   internal ratings based approachChapter 18   internal ratings based approach
Chapter 18 internal ratings based approach
Quan Risk
 
The Cross Section of Realized Stock Returns: The Pre-COMPUSTAT Evidence
The Cross Section of Realized Stock Returns: The Pre-COMPUSTAT EvidenceThe Cross Section of Realized Stock Returns: The Pre-COMPUSTAT Evidence
The Cross Section of Realized Stock Returns: The Pre-COMPUSTAT Evidence
Sudarshan Kadariya
 

La actualidad más candente (20)

Notes for Volatility Modeling lectures, Antoine Savine at Copenhagen University
Notes for Volatility Modeling lectures, Antoine Savine at Copenhagen UniversityNotes for Volatility Modeling lectures, Antoine Savine at Copenhagen University
Notes for Volatility Modeling lectures, Antoine Savine at Copenhagen University
 
60 Years Birthday, 30 Years of Ground Breaking Innovation: A Tribute to Bruno...
60 Years Birthday, 30 Years of Ground Breaking Innovation: A Tribute to Bruno...60 Years Birthday, 30 Years of Ground Breaking Innovation: A Tribute to Bruno...
60 Years Birthday, 30 Years of Ground Breaking Innovation: A Tribute to Bruno...
 
Stabilise risks of discontinuous payoffs with Fuzzy Logic by Antoine Savine
Stabilise risks of discontinuous payoffs with Fuzzy Logic by Antoine SavineStabilise risks of discontinuous payoffs with Fuzzy Logic by Antoine Savine
Stabilise risks of discontinuous payoffs with Fuzzy Logic by Antoine Savine
 
Ni marsa ipo_014_2016
Ni marsa ipo_014_2016Ni marsa ipo_014_2016
Ni marsa ipo_014_2016
 
Chapter 18 internal ratings based approach
Chapter 18   internal ratings based approachChapter 18   internal ratings based approach
Chapter 18 internal ratings based approach
 
Practical Implementation of AAD by Antoine Savine, Brian Huge and Hans-Jorgen...
Practical Implementation of AAD by Antoine Savine, Brian Huge and Hans-Jorgen...Practical Implementation of AAD by Antoine Savine, Brian Huge and Hans-Jorgen...
Practical Implementation of AAD by Antoine Savine, Brian Huge and Hans-Jorgen...
 
Differential Machine Learning Masterclass
Differential Machine Learning MasterclassDifferential Machine Learning Masterclass
Differential Machine Learning Masterclass
 
Contract Theory - The Nobel Prize in Economic Sciences 2016
Contract Theory - The Nobel Prize in Economic Sciences 2016Contract Theory - The Nobel Prize in Economic Sciences 2016
Contract Theory - The Nobel Prize in Economic Sciences 2016
 
Etude de la convergence du modèle binomial vers le modèle de Black Scholes
Etude de la convergence du modèle  binomial vers le modèle de Black ScholesEtude de la convergence du modèle  binomial vers le modèle de Black Scholes
Etude de la convergence du modèle binomial vers le modèle de Black Scholes
 
The Cross Section of Realized Stock Returns: The Pre-COMPUSTAT Evidence
The Cross Section of Realized Stock Returns: The Pre-COMPUSTAT EvidenceThe Cross Section of Realized Stock Returns: The Pre-COMPUSTAT Evidence
The Cross Section of Realized Stock Returns: The Pre-COMPUSTAT Evidence
 
Les techniques de couvertures internes contre le risque de change
Les techniques de couvertures internes contre le risque de changeLes techniques de couvertures internes contre le risque de change
Les techniques de couvertures internes contre le risque de change
 
Impact of Valuation Adjustments (CVA, DVA, FVA, KVA) on Bank's Processes - An...
Impact of Valuation Adjustments (CVA, DVA, FVA, KVA) on Bank's Processes - An...Impact of Valuation Adjustments (CVA, DVA, FVA, KVA) on Bank's Processes - An...
Impact of Valuation Adjustments (CVA, DVA, FVA, KVA) on Bank's Processes - An...
 
Lf 2020 skew
Lf 2020 skewLf 2020 skew
Lf 2020 skew
 
Le rôle de la monnaie et du crédit
Le rôle de la monnaie et du créditLe rôle de la monnaie et du crédit
Le rôle de la monnaie et du crédit
 
XVA
XVAXVA
XVA
 
Real-time applications on IntelXeon/Phi
Real-time applications on IntelXeon/PhiReal-time applications on IntelXeon/Phi
Real-time applications on IntelXeon/Phi
 
Probabilités et statistiques 2ème partie
Probabilités et statistiques   2ème partieProbabilités et statistiques   2ème partie
Probabilités et statistiques 2ème partie
 
Risk aversion
Risk aversionRisk aversion
Risk aversion
 
Gestion de la trésorerie et risque de change
Gestion de la trésorerie et risque de changeGestion de la trésorerie et risque de change
Gestion de la trésorerie et risque de change
 
Presentation seminaire 10:05 ppt au laboratoire I3M
Presentation seminaire 10:05 ppt au laboratoire  I3MPresentation seminaire 10:05 ppt au laboratoire  I3M
Presentation seminaire 10:05 ppt au laboratoire I3M
 

Destacado

Capitolo 2 elementi di programmazione in vba
Capitolo 2   elementi di programmazione in vbaCapitolo 2   elementi di programmazione in vba
Capitolo 2 elementi di programmazione in vba
Giovanni Della Lunga
 
Capitolo 1 richiami mat. finanziaria
Capitolo 1   richiami mat. finanziariaCapitolo 1   richiami mat. finanziaria
Capitolo 1 richiami mat. finanziaria
Giovanni Della Lunga
 
Capitolo 3 anagrafica titoli e mercati finanziari
Capitolo 3   anagrafica titoli e mercati finanziariCapitolo 3   anagrafica titoli e mercati finanziari
Capitolo 3 anagrafica titoli e mercati finanziari
Giovanni Della Lunga
 
Capitolo 6a elementi di valutazione dei prodotti derivati
Capitolo 6a   elementi di valutazione dei prodotti derivatiCapitolo 6a   elementi di valutazione dei prodotti derivati
Capitolo 6a elementi di valutazione dei prodotti derivati
Giovanni Della Lunga
 
Modelli matematici rischio credito
Modelli matematici rischio creditoModelli matematici rischio credito
Modelli matematici rischio credito
Giovanni Della Lunga
 

Destacado (20)

Capitolo 2 elementi di programmazione in vba
Capitolo 2   elementi di programmazione in vbaCapitolo 2   elementi di programmazione in vba
Capitolo 2 elementi di programmazione in vba
 
Lezione 1 - Introduzione al VBA per Excel
Lezione 1 - Introduzione al VBA per ExcelLezione 1 - Introduzione al VBA per Excel
Lezione 1 - Introduzione al VBA per Excel
 
Lezione 3 metodo monte carlo
Lezione 3   metodo monte carloLezione 3   metodo monte carlo
Lezione 3 metodo monte carlo
 
Capitolo 1 richiami mat. finanziaria
Capitolo 1   richiami mat. finanziariaCapitolo 1   richiami mat. finanziaria
Capitolo 1 richiami mat. finanziaria
 
Capitolo 3 anagrafica titoli e mercati finanziari
Capitolo 3   anagrafica titoli e mercati finanziariCapitolo 3   anagrafica titoli e mercati finanziari
Capitolo 3 anagrafica titoli e mercati finanziari
 
Simulation methods finance_1
Simulation methods finance_1Simulation methods finance_1
Simulation methods finance_1
 
From real to risk neutral probability measure for pricing and managing cva
From real to risk neutral probability measure for pricing and managing cvaFrom real to risk neutral probability measure for pricing and managing cva
From real to risk neutral probability measure for pricing and managing cva
 
Capitolo 6a elementi di valutazione dei prodotti derivati
Capitolo 6a   elementi di valutazione dei prodotti derivatiCapitolo 6a   elementi di valutazione dei prodotti derivati
Capitolo 6a elementi di valutazione dei prodotti derivati
 
Modelli matematici rischio credito
Modelli matematici rischio creditoModelli matematici rischio credito
Modelli matematici rischio credito
 
E-QuanT(TimeSeries)
E-QuanT(TimeSeries)E-QuanT(TimeSeries)
E-QuanT(TimeSeries)
 
Workshop 2013 of Quantitative Finance
Workshop 2013 of Quantitative FinanceWorkshop 2013 of Quantitative Finance
Workshop 2013 of Quantitative Finance
 
Metodi numerici
Metodi numericiMetodi numerici
Metodi numerici
 
Credit Value Adjustment in the Extended Structural Default Model
Credit Value Adjustment in the Extended Structural Default ModelCredit Value Adjustment in the Extended Structural Default Model
Credit Value Adjustment in the Extended Structural Default Model
 
The comparative study of finite difference method and monte carlo method for ...
The comparative study of finite difference method and monte carlo method for ...The comparative study of finite difference method and monte carlo method for ...
The comparative study of finite difference method and monte carlo method for ...
 
Workshop 2011 of Quantitative Finance
Workshop 2011 of Quantitative FinanceWorkshop 2011 of Quantitative Finance
Workshop 2011 of Quantitative Finance
 
Workshop 2012 of Quantitative Finance
Workshop 2012 of Quantitative FinanceWorkshop 2012 of Quantitative Finance
Workshop 2012 of Quantitative Finance
 
Alternating direction-implicit-finite-difference-method-for-transient-2 d-hea...
Alternating direction-implicit-finite-difference-method-for-transient-2 d-hea...Alternating direction-implicit-finite-difference-method-for-transient-2 d-hea...
Alternating direction-implicit-finite-difference-method-for-transient-2 d-hea...
 
Global Derivatives 2014 - Did Basel put the final nail in the coffin of CSA D...
Global Derivatives 2014 - Did Basel put the final nail in the coffin of CSA D...Global Derivatives 2014 - Did Basel put the final nail in the coffin of CSA D...
Global Derivatives 2014 - Did Basel put the final nail in the coffin of CSA D...
 
Duration and Convexity
Duration and ConvexityDuration and Convexity
Duration and Convexity
 
CVA+FFVA+MV+Perspective.4
CVA+FFVA+MV+Perspective.4CVA+FFVA+MV+Perspective.4
CVA+FFVA+MV+Perspective.4
 

Similar a Simulation methods finance_2

香港六合彩
香港六合彩香港六合彩
香港六合彩
shujia
 
0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx
0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx
0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx
mercysuttle
 
The monte carlo method
The monte carlo methodThe monte carlo method
The monte carlo method
Saurabh Sood
 

Similar a Simulation methods finance_2 (20)

CVA In Presence Of Wrong Way Risk and Early Exercise - Chiara Annicchiarico, ...
CVA In Presence Of Wrong Way Risk and Early Exercise - Chiara Annicchiarico, ...CVA In Presence Of Wrong Way Risk and Early Exercise - Chiara Annicchiarico, ...
CVA In Presence Of Wrong Way Risk and Early Exercise - Chiara Annicchiarico, ...
 
High Dimensional Quasi Monte Carlo methods in Finance
High Dimensional Quasi Monte Carlo methods in FinanceHigh Dimensional Quasi Monte Carlo methods in Finance
High Dimensional Quasi Monte Carlo methods in Finance
 
High Dimensional Quasi Monte Carlo Method in Finance
High Dimensional Quasi Monte Carlo Method in FinanceHigh Dimensional Quasi Monte Carlo Method in Finance
High Dimensional Quasi Monte Carlo Method in Finance
 
香港六合彩
香港六合彩香港六合彩
香港六合彩
 
Leniency, Asymmetric Punishment and Corruption: Preliminary Evidence from China
Leniency, Asymmetric Punishment and Corruption: Preliminary Evidence from ChinaLeniency, Asymmetric Punishment and Corruption: Preliminary Evidence from China
Leniency, Asymmetric Punishment and Corruption: Preliminary Evidence from China
 
0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx
0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx
0132994879.DS_Store__MACOSX0132994879._.DS_Store01329.docx
 
Pres fibe2015-pbs-org
Pres fibe2015-pbs-orgPres fibe2015-pbs-org
Pres fibe2015-pbs-org
 
Pres-Fibe2015-pbs-Org
Pres-Fibe2015-pbs-OrgPres-Fibe2015-pbs-Org
Pres-Fibe2015-pbs-Org
 
Asian basket options
Asian basket optionsAsian basket options
Asian basket options
 
Ingenieria economica
Ingenieria economicaIngenieria economica
Ingenieria economica
 
presentation
presentationpresentation
presentation
 
Levy models
Levy modelsLevy models
Levy models
 
3. Finance
3. Finance3. Finance
3. Finance
 
Unifying Technical Analysis and Statistical Arbitrage
Unifying Technical Analysis and Statistical ArbitrageUnifying Technical Analysis and Statistical Arbitrage
Unifying Technical Analysis and Statistical Arbitrage
 
Damien lamberton, bernard lapeyre, nicolas rabeau
Damien lamberton, bernard lapeyre, nicolas rabeauDamien lamberton, bernard lapeyre, nicolas rabeau
Damien lamberton, bernard lapeyre, nicolas rabeau
 
The monte carlo method
The monte carlo methodThe monte carlo method
The monte carlo method
 
Business
BusinessBusiness
Business
 
Stanford CME 241 - Reinforcement Learning for Stochastic Control Problems in ...
Stanford CME 241 - Reinforcement Learning for Stochastic Control Problems in ...Stanford CME 241 - Reinforcement Learning for Stochastic Control Problems in ...
Stanford CME 241 - Reinforcement Learning for Stochastic Control Problems in ...
 
Notes part iii
Notes   part iiiNotes   part iii
Notes part iii
 
Copule slides
Copule slidesCopule slides
Copule slides
 

Más de Giovanni Della Lunga

Más de Giovanni Della Lunga (20)

Halloween Conference 2023 - Introduction to Deep Learning
Halloween Conference 2023 - Introduction to Deep LearningHalloween Conference 2023 - Introduction to Deep Learning
Halloween Conference 2023 - Introduction to Deep Learning
 
Excel development e sql 3.9
Excel development e sql   3.9Excel development e sql   3.9
Excel development e sql 3.9
 
Excel development e sql 1.7
Excel development e sql   1.7Excel development e sql   1.7
Excel development e sql 1.7
 
Introduction to python programming 2
Introduction to python programming   2Introduction to python programming   2
Introduction to python programming 2
 
Introduction to python programming 1
Introduction to python programming   1Introduction to python programming   1
Introduction to python programming 1
 
Excel development e sql 2.1
Excel development e sql   2.1Excel development e sql   2.1
Excel development e sql 2.1
 
Excel development e sql 1.3
Excel development e sql   1.3Excel development e sql   1.3
Excel development e sql 1.3
 
Cavalcando onde gravitazionali
Cavalcando onde gravitazionaliCavalcando onde gravitazionali
Cavalcando onde gravitazionali
 
Viaggi nel tempo [2015 01 24]
Viaggi nel tempo [2015 01 24]Viaggi nel tempo [2015 01 24]
Viaggi nel tempo [2015 01 24]
 
Universo lato oscuro
Universo lato oscuroUniverso lato oscuro
Universo lato oscuro
 
Breve intro caos
Breve intro caosBreve intro caos
Breve intro caos
 
Fg esercizi 4
Fg esercizi 4Fg esercizi 4
Fg esercizi 4
 
2 magnetismo
2 magnetismo2 magnetismo
2 magnetismo
 
1 elettrostatica
1 elettrostatica1 elettrostatica
1 elettrostatica
 
Fenomeni termici
Fenomeni termiciFenomeni termici
Fenomeni termici
 
1 meccanica fluidi
1 meccanica fluidi1 meccanica fluidi
1 meccanica fluidi
 
1 spazio tempo_movimento
1 spazio tempo_movimento1 spazio tempo_movimento
1 spazio tempo_movimento
 
2 principi dinamica
2 principi dinamica2 principi dinamica
2 principi dinamica
 
3 energia
3 energia3 energia
3 energia
 
Cinetica
CineticaCinetica
Cinetica
 

Último

VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...
VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...
VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...
dipikadinghjn ( Why You Choose Us? ) Escorts
 
CALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual service
CALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual serviceCALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual service
CALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual service
anilsa9823
 
VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...
VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...
VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...
dipikadinghjn ( Why You Choose Us? ) Escorts
 

Último (20)

VVIP Pune Call Girls Katraj (7001035870) Pune Escorts Nearby with Complete Sa...
VVIP Pune Call Girls Katraj (7001035870) Pune Escorts Nearby with Complete Sa...VVIP Pune Call Girls Katraj (7001035870) Pune Escorts Nearby with Complete Sa...
VVIP Pune Call Girls Katraj (7001035870) Pune Escorts Nearby with Complete Sa...
 
TEST BANK For Corporate Finance, 13th Edition By Stephen Ross, Randolph Weste...
TEST BANK For Corporate Finance, 13th Edition By Stephen Ross, Randolph Weste...TEST BANK For Corporate Finance, 13th Edition By Stephen Ross, Randolph Weste...
TEST BANK For Corporate Finance, 13th Edition By Stephen Ross, Randolph Weste...
 
VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...
VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...
VIP Call Girl Service Andheri West ⚡ 9920725232 What It Takes To Be The Best ...
 
Solution Manual for Financial Accounting, 11th Edition by Robert Libby, Patri...
Solution Manual for Financial Accounting, 11th Edition by Robert Libby, Patri...Solution Manual for Financial Accounting, 11th Edition by Robert Libby, Patri...
Solution Manual for Financial Accounting, 11th Edition by Robert Libby, Patri...
 
CALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual service
CALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual serviceCALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual service
CALL ON ➥8923113531 🔝Call Girls Gomti Nagar Lucknow best sexual service
 
Top Rated Pune Call Girls Viman Nagar ⟟ 6297143586 ⟟ Call Me For Genuine Sex...
Top Rated  Pune Call Girls Viman Nagar ⟟ 6297143586 ⟟ Call Me For Genuine Sex...Top Rated  Pune Call Girls Viman Nagar ⟟ 6297143586 ⟟ Call Me For Genuine Sex...
Top Rated Pune Call Girls Viman Nagar ⟟ 6297143586 ⟟ Call Me For Genuine Sex...
 
Basic concepts related to Financial modelling
Basic concepts related to Financial modellingBasic concepts related to Financial modelling
Basic concepts related to Financial modelling
 
The Economic History of the U.S. Lecture 22.pdf
The Economic History of the U.S. Lecture 22.pdfThe Economic History of the U.S. Lecture 22.pdf
The Economic History of the U.S. Lecture 22.pdf
 
The Economic History of the U.S. Lecture 18.pdf
The Economic History of the U.S. Lecture 18.pdfThe Economic History of the U.S. Lecture 18.pdf
The Economic History of the U.S. Lecture 18.pdf
 
06_Joeri Van Speybroek_Dell_MeetupDora&Cybersecurity.pdf
06_Joeri Van Speybroek_Dell_MeetupDora&Cybersecurity.pdf06_Joeri Van Speybroek_Dell_MeetupDora&Cybersecurity.pdf
06_Joeri Van Speybroek_Dell_MeetupDora&Cybersecurity.pdf
 
00_Main ppt_MeetupDORA&CyberSecurity.pptx
00_Main ppt_MeetupDORA&CyberSecurity.pptx00_Main ppt_MeetupDORA&CyberSecurity.pptx
00_Main ppt_MeetupDORA&CyberSecurity.pptx
 
The Economic History of the U.S. Lecture 23.pdf
The Economic History of the U.S. Lecture 23.pdfThe Economic History of the U.S. Lecture 23.pdf
The Economic History of the U.S. Lecture 23.pdf
 
03_Emmanuel Ndiaye_Degroof Petercam.pptx
03_Emmanuel Ndiaye_Degroof Petercam.pptx03_Emmanuel Ndiaye_Degroof Petercam.pptx
03_Emmanuel Ndiaye_Degroof Petercam.pptx
 
(INDIRA) Call Girl Mumbai Call Now 8250077686 Mumbai Escorts 24x7
(INDIRA) Call Girl Mumbai Call Now 8250077686 Mumbai Escorts 24x7(INDIRA) Call Girl Mumbai Call Now 8250077686 Mumbai Escorts 24x7
(INDIRA) Call Girl Mumbai Call Now 8250077686 Mumbai Escorts 24x7
 
VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...
VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...
VIP Independent Call Girls in Andheri 🌹 9920725232 ( Call Me ) Mumbai Escorts...
 
Booking open Available Pune Call Girls Shivane 6297143586 Call Hot Indian Gi...
Booking open Available Pune Call Girls Shivane  6297143586 Call Hot Indian Gi...Booking open Available Pune Call Girls Shivane  6297143586 Call Hot Indian Gi...
Booking open Available Pune Call Girls Shivane 6297143586 Call Hot Indian Gi...
 
02_Fabio Colombo_Accenture_MeetupDora&Cybersecurity.pptx
02_Fabio Colombo_Accenture_MeetupDora&Cybersecurity.pptx02_Fabio Colombo_Accenture_MeetupDora&Cybersecurity.pptx
02_Fabio Colombo_Accenture_MeetupDora&Cybersecurity.pptx
 
(Vedika) Low Rate Call Girls in Pune Call Now 8250077686 Pune Escorts 24x7
(Vedika) Low Rate Call Girls in Pune Call Now 8250077686 Pune Escorts 24x7(Vedika) Low Rate Call Girls in Pune Call Now 8250077686 Pune Escorts 24x7
(Vedika) Low Rate Call Girls in Pune Call Now 8250077686 Pune Escorts 24x7
 
Log your LOA pain with Pension Lab's brilliant campaign
Log your LOA pain with Pension Lab's brilliant campaignLog your LOA pain with Pension Lab's brilliant campaign
Log your LOA pain with Pension Lab's brilliant campaign
 
Solution Manual for Principles of Corporate Finance 14th Edition by Richard B...
Solution Manual for Principles of Corporate Finance 14th Edition by Richard B...Solution Manual for Principles of Corporate Finance 14th Edition by Richard B...
Solution Manual for Principles of Corporate Finance 14th Edition by Richard B...
 

Simulation methods finance_2

  • 1. Introduction to Monte Carlo in Finance Giovanni Della Lunga WORKSHOP IN QUANTITATIVE FINANCE Bologna - May 12-13, 2016 Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 1 / 79
  • 2. Valuation of American Option Outline 1 Valuation of American Option 2 The Hull and White Model 3 MCS for CVA Estimation Definitions CVA of a Plain Vanilla Swap: the Analytical Model CVA of a Plain Vanilla Swap: the Simulation Approach Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 2 / 79
  • 3. Valuation of American Option Valuation of American Option by Simulation As we have seen Monte Carlo simulation is a flexible and powerful numerical method to value financial derivatives of any kind. However being a forward evolving technique, it is per se not suited to address the valuation of American or Bermudan options which are valued in general by backwards induction. Longstaff and Schwartz provide a numerically efficient method to resolve this problem by what they call Least-Squares Monte Carlo. The problem with Monte Carlo is that the decision to exercise an American option or not is dependent on the continuation value. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 3 / 79
  • 4. Valuation of American Option Valuation of American Option by Simulation Consider a simulation with M + 1 points in time and I paths. Given a simulated index level St,i , t ∈ {0, ..., T}, i ∈ {1, ..., I}, what is the continuation value Ct,i (St,i ), i.e. the expected payoff of not exercising the option? The approach of Longstaff-Schwartz approximates continuation values for American options in the backwards steps by an ordinary least-squares regression. Equipped with such approximations, the option is exercised if the approximate continuation value is lower than the value of immediate exercise. Otherwise it is not exercised. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 4 / 79
  • 5. Valuation of American Option Valuation of American Option by Simulation In order to explain the metodology, let’s start from a simpler problem. Consider a bermudan option which is similar to an american option, except that it can be early exercised once only on a specific set of dates. In the next figure, we can represent the schedule of a put bermudan option with strike K and maturity in 6 years. Each year you can choose whether to exercise or not ... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 5 / 79
  • 6. Valuation of American Option Valuation of American Option by Simulation Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 6 / 79
  • 7. Valuation of American Option Valuation of American Option by Simulation Let’s consider a simpler example: a put option which can be exercised early only once ... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 7 / 79
  • 8. Valuation of American Option Valuation of American Option by Simulation Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 8 / 79
  • 9. Valuation of American Option Valuation of American Option by Simulation Can we price this product by means of a Monte Carlo? Yes we can! Let’s see how. Let’s implement a MC which actually simulates, besides the evolution of the market, what an investor holding this option would do (clearly an investor who lives in the risk neutral world). In the following example we will assume the following data, S(T) =, K =, r =, σ =, t1 = 1y, T = 2y. We simulate that 1y has passed, computing the new value of the asset and the new value of the money market account S(t1 = 1y) = S(t0)e(r−1 2 σ2)(t1−t0)+σ √ t1−t0N(0,1) B(t1 = 1y) = B(t0)er(t1−t0) Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 9 / 79
  • 10. Valuation of American Option Valuation of American Option by Simulation At this point the investor could exercise. How does he know if it is convenient? In case of exercise he knows exactly the payoff he’s getting. In case he continues, he knows that it is the same of having a European Put Option. So, in mathematical terms we have the following payoff in t1 max [K − S(t1), P(t1, T; S(t1), K)] where P(t1, T; S(t1), K) is the price of a Put which we compute analytically! In the jargon of american products, P is called the continuation value, i.e. the value of holding the option instead of early exercising it. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 10 / 79
  • 11. Valuation of American Option Valuation of American Option by Simulation So the premium of the option is the average of this discounted payoff calculated in each iteration of the Monte Carlo procedure. 1 N i max [K − Si (t1), P(t1, T; Si (t1), K)] Some considerations are in order. We could have priced this product because we have an analytical pricing formula for the put. What if we didn’t have it? Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 11 / 79
  • 12. Valuation of American Option Valuation of American Option by Simulation Brute force solution: for each realization of S(t1) we run another Monte Carlo to price the put. This method (called Nested Monte Carlo) is very time consuming. For this very simple case it’s time of execution grows as N2, which becomes prohibitive when you deal with more than one exercise date! Let’s search for a finer solution analyzing the relationship between the continuation value (in this very simple example) and the simulated realization of S at step t1. let’s plot the discounted payoff at maturity, Pi , versus Si (t1) ... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 12 / 79
  • 13. Valuation of American Option Valuation of American Option by Simulation Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 13 / 79
  • 14. Valuation of American Option Valuation of American Option by Simulation Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 14 / 79
  • 15. Valuation of American Option As you can see, the analytical price of the put is a curve which kinds of interpolate the cloud of Monte Carlo points. This suggest us that the price at time t1 can be computed by means of an average on all discounted payoff (i.e. the barycentre of the cloud made of discounted payoff) So maybe... the future value of an option can be seen as the problem of finding the curve that best fits the cloud of discounted payoff (up to date of interest)!!! In the next slide, for example, there is a curve found by means of a linear regression on a polynomial of 5th order... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 15 / 79
  • 16. Valuation of American Option Valuation of American Option by Simulation Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 16 / 79
  • 17. Valuation of American Option Valuation of American Option by Simulation Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 17 / 79
  • 18. Valuation of American Option Valuation of American Option by Simulation We now have an empirical pricing formula for the put to be used in my MCS P(t1, T, S(t1), K) = c0 + c1S(t1) + c2S(t1)2 + c3S(t1)3 + c4S(t1)4 + c5S(t1)5 The formula is obviously fast, the cost of the algorithm being the best fit. Please note that we could have used any form for the curve (not only a plynomial). This method has the advantage that it can be solved as a linear regression, which is fast. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 18 / 79
  • 19. Valuation of American Option The Longstaff-Schwartz Algorithm The major insight of Longstaff-Schwartz is to estimate the continuation value Ct,i by ordinary least-squares regression, therefore the name ”Least Square Monte Carlo” for their algorithm; They propose to regress the I continuation values Yt,i against the I simulated index levels St,i . Given D basis functions b with b1, . . . , bD : RD → R for the regression, the continuation value Ct,i is according to their approach approximated by: Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 19 / 79
  • 20. Valuation of American Option The Longstaff-Schwartz Algorithm Given D basis functions b with b1, . . . , bD : RD → R for the regression, the continuation value Ct,i is according to their approach approximated by: ˆCt,i = D d=1 αd,tbd (St,i ) (1) The optimal regression parameters αd,t are the result of the minimization min α1,t ,...,αD,t 1 I I i=1 Yt,i − D d=1 αd,tbd (St,i ) 2 Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 20 / 79
  • 21. Valuation of American Option The Longstaff-Schwartz Algorithm Simulate I index level paths with M + 1 points in time leading to index level values St,i , t ∈ {0, ..., T}, i ∈ {1, ..., I}; For t = T the option value is VT,i = hT (ST,i ) by arbitrage Start iterating backwards t = T − ∆t, . . . , ∆t: regress the Tt,i against the St,i , i ∈ {1, . . . , I}, given D basis function b approximate Ct,i by ˆCt,i according to (1) given the optimal parameters αd,t from (2) set Vt,i = ht(St,i ) if ht(St,i ) > ˆCt,i exercise takes place Yt,i if ht(St,i ) ≤ ˆCt,i no exercise takes place repeat iteration steps until t = ∆t; for t = 0 calculate the LSM estimator ˆV LSM 0 = e−r∆t 1 I I i=1 V∆t,i Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 21 / 79
  • 22. Valuation of American Option Notebook GitHub : polyhedron-gdl; Notebook : mcs american; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 22 / 79
  • 23. The Hull and White Model Outline 1 Valuation of American Option 2 The Hull and White Model 3 MCS for CVA Estimation Definitions CVA of a Plain Vanilla Swap: the Analytical Model CVA of a Plain Vanilla Swap: the Simulation Approach Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 23 / 79
  • 24. The Hull and White Model Hull-White Model Described by the SDE for the short rate dr = (θ(t) − ar)dt + σdw (1) See Brigo-Mercurio ... Our version simplified: a and σ constant; AKA Extended Vasicek (Note: r(t) is Gaussian); θ determined uniquely by term structure; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 24 / 79
  • 25. The Hull and White Model Hull-White Model: Solving for r(t) d(eat r) = eat dr + aeat rdt = θ(t)eat + eat σdw integrating both sides we obtain eat r(t) = r(0) + t 0 θ(s)eas ds + σ t 0 eas dw(s) simplify r(t) = r(0)e−at + t 0 θ(s)e−a(t−s) ds + σ t 0 e−a(t−s) dw(s) Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 25 / 79
  • 26. The Hull and White Model Hull-White Model: Solving for P(t,T) P(t, T) = V (t, r(t)) where V solves the PDE Vt + (θ(t) − ar)Vr + 1 2 σ2 Vrr − rV = 0 Final-time condition V (T, r) = 1 for all r at t = T; Ansatz: V = A(t, T)e−B(t,T)r(t) A and B must satisfy: At − θ(t)AB + 1 2 σ2 (AB)2 = 0, and Bt − aB + 1 = 0 Final-time conditions A(T, T) = 1 and B(T, T) = 0 Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 26 / 79
  • 27. The Hull and White Model Hull-White Model: Solving for P(t,T) B independent of θ so B(t, T) = 1 a 1 − e−a(T−t) (2) Solving for A requires integration of θ A(t, T) = exp  − T t θ(s)B(s, T)ds − σ2 2a2 (B(t, T) − T + t) − σ2 4a B(t, T)2   Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 27 / 79
  • 28. The Hull and White Model Hull-White Model: Determining θ Determining θ from the term structure at time 0; Goal: demonstrate the relation θ(t) = ∂f f ∂T (0, t) + af (0, t) + σ2 2a (1 − e−2at ) (3) Recall f (t, T) = −∂ log P(t, T)/∂T Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 28 / 79
  • 29. The Hull and White Model Hull-White Model: Determining θ We have − log P(0, T) = T 0 θ(s)B(s, T)ds + σ2 2a2 [B(0, T) − T] + σ2 4a B(0, T)2 + B(0, T)r0 Differentiating and using that B(T, T) = 1 and ∂T B − 1 = −aB we get f (0, T) = T 0 θ(s)∂T B(s, T)ds− σ2 2a2 B(0, T)+ σ2 2a2 B(0, T)∂T B(0, T)+∂T B(0, T)r0 Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 29 / 79
  • 30. The Hull and White Model Hull-White Model: Determining θ Differentiating again, get: ∂T f (0, T) = θ(T) + T 0 θ(s)∂TT B(s, T)ds − σ2 2a2 ∂T B(0, T) + σ2 2a2 [(∂T B(0, T))2 + B(0, T)∂TT B(0, T)] + ∂TT B(0, T)r0 (4) Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 30 / 79
  • 31. The Hull and White Model Hull-White Model: Determining θ Combine these equations, and use a∂T B + ∂TT B = 0; Get: af (0, T) + ∂T f (0, T) = θ(T) − σ2 2a (aB + ∂T B) + σ2 2a [aB∂T B + (∂T B)2 + B∂TT B] Substitute formula for B and simplify to get af (0, T) + ∂T f (0, T) = θ(T) − σ2 2a (1 − e−2aT ) QED Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 31 / 79
  • 32. The Hull and White Model Additive Factor Gaussian Model The model is given by dynamics (Brigo-Mercurio p. 143): r(t) = x(t) + φ(t) where dx(t) = −ax(t)dt + σdWt x(0) = 0 and φ is a deterministic shift which is added in order to fit exactly the initial zero coupon curve Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 32 / 79
  • 33. The Hull and White Model Additive Factor Gaussian Model So the short rate r(t) is distributed normally with mean and variance given by (Brigo-Mercurio p.144 equations 4.6 with η = 0) E(rt|rs) = x(s)e−a(t−s) + φ(t) Var(rt|rs) = σ2 2a 1 − e−2a(t−s) where φ(T) = f M(0, T) + σ2 2a 1 − e−aT 2 and f M(0, T) is the market instantaneous forward rate at time t as seen at time 0. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 33 / 79
  • 34. The Hull and White Model Additive Factor Gaussian Model Model discount factors are calculated as in Brigo-Mercurio (section 4.2): P(t, T) = PM(0, T) PM(0, t) exp (A(t, T)) A(t, T) = 1 2 [V (t, T) − V (0, T) + V (0, t)] − 1 − e−a(T−t) a x(t) where V (t, T) = σ2 a2 T − t + 2 a e−a(T−t) − 1 2a e−2a(T−t) − 3 2a Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 34 / 79
  • 35. MCS for CVA Estimation Outline 1 Valuation of American Option 2 The Hull and White Model 3 MCS for CVA Estimation Definitions CVA of a Plain Vanilla Swap: the Analytical Model CVA of a Plain Vanilla Swap: the Simulation Approach Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 35 / 79
  • 36. MCS for CVA Estimation Definitions Counterparty Risk In general a given company, say a financial institution A, will have portfolios with many other counterparties, varying among sovereign entities, corporates, hedge funds, insurance companies; Counterparty credit exposure is the amount a company, say A, could potentially lose in the event of one of its counterparties defaulting. As we’ll see in more details, it can be computed by simulating in different scenarios and at different times in the future, the price of the transactions with the given counterparty, and then by using some chosen statistic to characterise the price distributions that have been generated. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 36 / 79
  • 37. MCS for CVA Estimation Definitions CVA Context Counterparty risk can be considered broadly from two different points of view; The first point of view is risk management, leading to capital requirements revision, trading limits discussions and so on; The second point of view is valuation or pricing, leading to amounts called Credit Valuation Adjustment (CVA) and extensions thereof, including netting, collateral, re-hypothecation, close-out specification, wrong way risk and funding cost; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 37 / 79
  • 38. MCS for CVA Estimation Definitions Example: CVA of plain vanilla Interest-Rate Swap Consider counterparties A and B who enter into an interest-rate swap where A receives every six months the 6-month Libor rate on a notional of 100 million euro, while paying to B a fixed amount equal to the par 10-year swap rate on the same notional observed at inception. This is a typical swap contract with value zero at inception. As time passes and market conditions change, the value of the swap changes accordingly. Thus, if the swap rate decreases (resp. increases), the transaction will be out of the money (resp. in the money) as seen from A’s point of view. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 38 / 79
  • 39. MCS for CVA Estimation Definitions Example: CVA of plain vanilla Interest-Rate Swap Therefore, if B were to default at a point in the life of the trade when swap rates had increased, then A would need to replace in the market—at higher cost than the fixed amount being paid to B—the floating cashflows promised and not delivered by B. To compute the credit exposure for the swap, we would need to estimate the values the swap could take in different market scenarios at points in the future. For practical reason it can be useful to characterise the distribution of values with some quantity which can be useful for various risk controlling; For example we could compute the so called Expected Positive Exposure (more in the following) as EPEt = E[V + t ] Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 39 / 79
  • 40. MCS for CVA Estimation Definitions Exposure Profile: EPE Figure shows the EPE of the swap price distribution, over its entire life, as seen from party A’s point of view. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 40 / 79
  • 41. MCS for CVA Estimation Definitions Exposure Profile: Value Density Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 41 / 79
  • 42. MCS for CVA Estimation Definitions Exposure Profile Figure shows the full price distribution over time. The fair value for the swap, and this must therefore have value (and hence exposure level) identically equal to zero at inception. Similarly, towards the end of the transaction, when all payments but one due under the swap have been paid, the exposure remaining is that from only a single coupon exchange. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 42 / 79
  • 43. MCS for CVA Estimation Definitions Exposure Profile This explains what happens at the right end of the profile. At intermediate times, the shape of the profile is the result of opposing effects. On the one hand, as the interest rates underlying the swap diffuse, there is more variability in the realised Libor rates, potentially leading to higher exposure. On the other hand, as time evolves there are fewer payments remaining under the swap, and this mitigates the effect of diffusing rates. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 43 / 79
  • 44. MCS for CVA Estimation Definitions Exposure Profiles So there are two main effects that determine the credit exposure over time for a single transaction or for a portfolio of transactions with the same counterparty: diffusion and amortization; as time passes, the ”diffusion effect” tends to increase the exposure, since there is greater variability and, hence, greater potential for market price factors to move significantly away fro current levels; the ”amortization effect”, in contrast, tends to decrease the exposure over time, because it reduces the remaining cash flows that are exposed to default; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 44 / 79
  • 45. MCS for CVA Estimation Definitions Exposure Profiles For single cash flow products, such as FX Forwards, the potential exposure peaks at the maturity of the transaction, because it is driven purely by ”diffusion effect”; on the other hand, for products with multiple cash flows, such as interest-rate swaps, the potential exposure usually peaks at one-third to one-half of the way into the life of the transaction; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 45 / 79
  • 46. MCS for CVA Estimation Definitions Credit Value Adjustment Credit Value Adjustment (CVA) is by definition the difference between the risk-free portfolio value and the true portfolio value that takes into account the possibility of a counterparty’s default; in other words CVA is the market value of counterparty credit risk; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 46 / 79
  • 47. MCS for CVA Estimation Definitions Credit Value Adjustment Assuming independence between exposure and counterparty’s credit quality greatly simplifies the analysis. under this assumption we can write CVA = (1 − R) T 0 EE (t)dPD(0, t) (5) where EE (t) is the risk-neutral discounted expected exposure (EE) given by EE (t) = EQ B0 Bt E(t) (6) Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 47 / 79
  • 48. MCS for CVA Estimation Definitions Credit Value Adjustment In general calculating discounted EE requires simulations; Exposure is simulated at a fixed set of simulation dates, therefore the integral in (5) has to be approximated by the sum: CVA = (1 − R) N i=1 EE (tk)PD(tk−1, tk) (7) Since expectation in (6) is risk-neutral, scenario models for all price factors should be arbitrage free; This is achieved by appropriate calibration of drifts and volatilities specified in the price-factor evolution model; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 48 / 79
  • 49. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula At valuation time t, and provided the counterparty has not defaulted before t, i.e. on {τ > t}, the price of our payoff with maturity T under counterparty risk is Et[¯Π(t, T)] = Et[Π(t, T)] − Et[LGD It≤τ≤T D(t, τ)(NPV (τ))+ ] positive counterparty-risk adjustment = Et[Π(t, T)] − UCVA(t, T) (8) with UCVA(t, T) = Et[LGD It≤τ≤T D(t, τ)(NPV (τ))+ ] = Et[LGD It≤τ≤T D(t, τ)EAD] (9) Where LGD = 1 − REC is the loss given default, and the recovery fraction REC is assumed to be deterministic. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 49 / 79
  • 50. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula It is clear that the value of a defaultable claim is the sum of the value of the corresponding default-free claim minus a positive adjustment. The positive adjustment to be subtracted is called (Unilateral) Credit Valuation Adjustment (CVA), and it is given by a call option (with zero strike) on the residual NPV at default, giving nonzero contribution only in scenario where τ ≤ T. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 50 / 79
  • 51. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula Counterparty risk thus adds and optionality level to the original payoff. This renders the counterparty risk payoff model dependent even when the original payoff is model independent. This implies, for example, that while the valuation of swaps without counterparty risk is model independent, requiring no dynamical model for the term structure (no volatility and correlations in particular), the valuation of swaps under counterpaty risk will require and interest rate model. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 51 / 79
  • 52. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula Now we explore the well known result that the component of the IRS price due to counterparty risk is the sum of swaption prices with different maturities, each weighted with the probability of defaulting around that maturity. Let us suppose that we are a default free counterparty ”B” entering a payer swap with a defaultable counterparty ”C”, exchanging fixed for floating payments at times Ta+1, . . . , Tb. Denote by βi the year fraction between Ti−1 and Ti , and by P(t, Ti ) the default-free zero coupon bond price at time t for maturity Ti . We take a unit notional on the swap. The contract requires us to pay a fixed rate K and to receive the floating rate L resetting one period earlier until the default time τ of ”B” or until final maturity T if τ > T. The fair forward-swap rate K at a given time t in a default-free market is the one which renders the swap zero-valued in t. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 52 / 79
  • 53. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula In the risk-free case the discounted payoff for a payer IRS is b i=a+1 D(t, Ti )βi (L(Ti−1, Ti ) − K) (10) and the forward swap rate rendering the contract fair is K = S(t; Ta, Tb) = Sa,b(t) = P(t, Ta) − P(t, Tb) b i=a+1 P(t, Ti )βi Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 53 / 79
  • 54. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula Of course if we consider the possibility that ”C” may default, the correct spread to be paid in the fixed leg is lower as we are willing to be rewarded for bearing this default risk. In particular we have UCVA(t, Tb) = LGD Et[Iτ≤Tb D(t, τ)(NPV (τ))+ ] = LGD Tb Ta PS (t; s, Tb, K, S(t; s, Tb), σs,Tb ) dsQ{τ ≤ s} (11) being PS (t; s, Tb, K, S(t; s, Tb), σs,Tb ) the price in t of a swaption with maturity s, strike K underlying forward swap rate S(t; s, Tb), volatility σs,Tb and underlying swap with final maturity Tb. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 54 / 79
  • 55. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula The proof is the following: given independence between τ and the interest rates, and given that the residual NPV is a forward start IRS starting at the default time, the option on the residual NPV is a sum of swaptions with maturities ranging the possible values of the default time, each weighted (thanks to the independence assumption) by the probabilities of defaulting around each time value. We can simplify formulas allow the default to happen only at points Ti of the fixed leg payment grid. In this way the expected loss part is simplified. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 55 / 79
  • 56. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model The General Unilateral Counterparty Risk Pricing Formula Indeed in the case of postponed (default occour to the first Ti following τ) payoff we obtain: UCVA(t, Tb) = LGD Et [Iτ≤Tb D(t, τ)(NPV (τ))+ ] = LGD b−1 i=a+1 PS (t; s, Tb, K, S(t; s, Tb), σs,Tb ) (Q{τ ≥ Ti } − Q{τ > Ti }) (12) Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 56 / 79
  • 57. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Analytical Model Notebook GitHub : polyhedron-gdl; Notebook : n09 cva swap; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 57 / 79
  • 58. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Monte Carlo Framework for CVA The industry practice to compute exposure is to use a simple Monte Carlo framework implemented in three steps: 1 scenario generation, 2 pricing 3 aggregation. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 58 / 79
  • 59. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Monte Carlo Framework for CVA The first step involves generating scenarios of the underlying risk factors at future points in time. Simple products can then be priced on each scenario and each time step, therefore generating empirical price distributions. From the price distribution at each time it is then possible to extract convenient statistical quantities. Exposure of portfolios can be computed by consistently pricing different products on the same underlying scenarios and aggregating the results taking into account possible netting and collateral agreement with the counterparty. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 59 / 79
  • 60. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Monte Carlo Framework for CVA If taken literally, this approach works only for relatively simple products which can be priced analytically, or which can be approximated in analytical form, and which do not need complex calibrations depending on market scenarios. More exotic products requiring relatively complex pricing, cannot be treated in this way. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 60 / 79
  • 61. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach CVA of a Plain Vanilla Swap: the Simulation Approach 1 Simulate yield curve at future dates 2 Calculate your derivatives portfolio NPV (net present value) at each time point for each scenario 3 Calculate CVA as sum of Expected Exposure multiplied by probability of default at this interval CVA = (1 − R) DF(t)EE(t)dQt where R is the Recovery Rate (normally set to 40%) EE(t) is the expected exposure at time t and dQt the survival probability density, DF(t) is the discount factor at time t. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 61 / 79
  • 62. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach CVA of a Plain Vanilla Swap: the Simulation Approach In this simple example we will use a modified version of Hull White model to generate future yield curves. In practice many banks use some yield curve evolution models based on this model. For each point of time we will generate whole yield curve based on short rate. Then we will price our interest rate swap on each of these curves; To approximate CVA we will use BASEL III formula for regulatory capital charge approximating default probability [or survival probability ] as exp(−ST /(1 − R)) so we get CVA = (1 − R) i EE(Ti ) + EE(Ti−1 2 e−S(Ti−1)/(1−R) − e−S(Ti )/(1−R) where EE is the discounted Expected Exposure of portfolio. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 62 / 79
  • 63. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach CVA of a Plain Vanilla Swap: the Simulation Approach Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 63 / 79
  • 64. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Notebook GitHub : polyhedron-gdl; Notebook : n10 mcs cva swap; Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 64 / 79
  • 65. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Implementation Challenges The Monte Carlo framework we have shown in the previous section, seems to give a good implementation recipe. For a given portfolio of transactions we could identify the underlying risk factors and simulate forward (or spot) prices, taking into account correlations if required, use functions already implemented to price each product, and then derive statistical quantities. As we have mentioned already, this could be the approach followed by a financial institution to assess the counterparty credit risk of its OTC derivatives portfolios. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 65 / 79
  • 66. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Implementation Challenges In the implementation phase, however, there can be issues which need to be addressed. The generation of correlated scenarios is not trivial, as there can be thousands of different risk factors driving the dynamics of products in the portfolio. Consider for example an equity portfolio, where each underlying stock needs, at least in principle, a specific simulation. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 66 / 79
  • 67. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Implementation Challenges Not all products can be computed in analytical form. Most exotics are priced on grids using PDEs or using Monte Carlo approaches. In these cases the exposure computation would require a Monte Carlo simulation for scenarios and a Monte Carlo simulation, or a PDE computation, for each scenario and time step to price the instrument. This becomes quickly unfeasible from a computational point of view. In addition, depending on the model used for pricing, calibration could also become problematic, as it has to be performed at each scenario. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 67 / 79
  • 68. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach American Monte Carlo The points highlighted in the previous section clearly show that the classical Monte Carlo scheme has intrinsic limitations and that we need an alternative approach. There are possibilities to circumvent in a systematic way some of the problems related to valuation and architecture. The basic idea is to approach the counterparty exposure problem as a pricing problem, and thus to use pricing algorithms, which generate not just the value of a trade at inception, but rather a price distribution at predetermined time steps. One possibility is to use the so called American Monte Carlo algorithm, which we will refer to as, simply, the AMC algorithm. The main feature of this algorithm is that, instead of building a price moving forward in time, it starts from maturity, where the value of the transaction is known, and goes backwards, till the inception. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 68 / 79
  • 69. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Let’s illustrate with a Bermuda Swaption which can be exercised at 2 dates, T1 and T2. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 69 / 79
  • 70. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Forward Phase: we diffuse risk factors and store in memory contract cash flows and payoff variables as the will be used in the Backward Phase. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 70 / 79
  • 71. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Backward Phase: we discount payoff contract and add cash flows up to T2. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 71 / 79
  • 72. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Backward Phase: At T2 we obtain a cloud of points... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 72 / 79
  • 73. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation ... regression is performed to obtain product fair value at T2 as a function of regression basis. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 73 / 79
  • 74. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation We discount to T1 obtaining a cloud of points (adding present cash flow from forward phase). Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 74 / 79
  • 75. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Regression is performed at T1 as a function of regression basis. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 75 / 79
  • 76. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Forward Phase: we then move forward again and invoke regression functions with the new set of MC paths ... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 76 / 79
  • 77. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation We can compute distribution of MTMs, exposure, EPE, PFE, etc... Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 77 / 79
  • 78. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach AMC CVA Simulation Recap Important Remark: In Phase 3, MC diffusion can be different from Phase 1. Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 78 / 79
  • 79. MCS for CVA Estimation CVA of a Plain Vanilla Swap: the Simulation Approach Credits Damiano Brigo, Fabio Mercurio ”Interest Rate Models — Theory and Practice” Springer Finance (2006) Damiano Brigo, Massimo Morini, Andrea Pallavicini ”Counterparty Credit Risk, Collateral and Funding” Wiley Finance (2013) Umberto Cherubini, Elisa Luciano, Walter Vecchiato ”Copula Methods in Finance” Wiley Finance (2004) Tommaso Gabbriellini ”American Options with Monte Carlo” Presentation on Slideshare Yves Hilpisch ”Derivatives Analytics with Python” Wiley Finance (2015) Don L. McLeish ”Monte Carlo Simulation and Finance” Wiley Finance (2005) Giovanni Della Lunga (WORKSHOP IN QUANTITATIVE FINANCE)Introduction to Monte Carlo in Finance Bologna - May 12-13, 2016 79 / 79