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Web Science and Technologies
                                          University of Koblenz–Landau, Germany



    Diversity Dynamics in
      Online Networks
 Jérôme Kunegis¹      Sergej Sizov¹       Felix Schwagereit¹     Damien Fay²

¹ University of Koblenz–Landau, Germany        ² University College Cork, Ireland

                        HT 2012, Milwaukee, WI
                            June 27, 2012
Everyone likes good things:




   Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   2
Or even better: Diversity!




    Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   3
Structural Diversity




 Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   4
(1) Length of paths

 Diversity                                     No diversity




“Large” world                              Small world

      Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   5
90-percentile effective diameter ±0.9


                                   Hop plot




       Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   6
“T
                                                  he
                                                         Wo
                                                           rld
                                                                       Ge
                                                                            ts
                                                                                  Sm
                                                                                     a   lle
                                                                                            r”




(Leskovec, Kleinberg & Faloutsos 2007)
                        Jérôme Kunegis et al.   Diversity Dynamics in Online Networks     7
Outline

(A) How can structural diversity be measured?
(B) How does diversity change?




         Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   8
(A) How to Measure Diversity in a Network?


      (1) Length of paths
      (2) Numbers of neighbors
      (3) Size of communities
      (4) Random walks
      (5) Controllability

          Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   9
(2) Number of neighbors

Diversity                                    No diversity




d(i) ¼ d(j)                                d(i)       ¿     d(j)

    Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   10
Gini Coefficient




Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   11
“The Rich Get Richer”




(Barabási & Albert 1999)
                       Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   12
(3) Size of communities
Diversity                                    No diversity




    Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   13
Fractional Rank

 Spectrum of the graph = f¸1, ¸2, ¸3, . . .g



rankF =   §k (¸k / ¸1)              2
                                        = (kAkF / kAk2)2




            Jérôme Kunegis et al.          Diversity Dynamics in Online Networks   14
“Eigenvector Preferential Attachment”

                        Ui1 Uj1 > ¸1 / 2jEj




Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   15
(4) Random walks
 Diversity                                     No diversity




Pret(L) large                                Pret(L) small

      Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   16
Weighted Spectral Distribution
Pret(L) = §(i, j, . . . k) (d(i) d(j) . . . d(k)){1
                  = tr(NL)
                  = § k ¸k L

where ¸k are eigenvalues of N = D{1/2 A D{1/2.


          Here: Use L = 4 and k · R

             Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   17
Eigenvalues of N




  Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   18
“R
          an
            do
                        m
                            Wa
                                 lks
                                       Ar
                                         riv
                                                eL
                                                       es
                                                         sO
                                                           ft e
                                                                     n”




Jérôme Kunegis et al.        Diversity Dynamics in Online Networks   19
(5) Controllability
Diversity                                    No diversity




                                  (Liu, Slotine & Barabási 2011)


    Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   20
Find a maximal directed 2-matching




   #Knobs needed = jVj { max jMj 
      Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   21
“Ne
                        two
                           rks
                                 Get
                                       E as
                                           ier
                                               to C
                                                    ont
                                                        rol”




Jérôme Kunegis et al.        Diversity Dynamics in Online Networks   22
(B) Experiments
       20 networks from konect.uni-koblenz.de

       9 authorship, 3 communication, 3 social, 3
       interaction, 1 rating, 1 physical
Measure                                         Diversity     No diversity          Diversity
                                               decreasing        trend             increasing
(1) Diameter                                       12                8                      0
(2) Gini coefficient                               13                3                      5
(3) Fractional rank                                10                6                      4
(4) Weighted spectral distribution                 12                7                      1
(5) Controllability                                15                5                      0


                       Jérôme Kunegis et al.        Diversity Dynamics in Online Networks       23
Thank You
Jérôme Kunegis                                               @kunegis
Sergej Sizov
Felix Schwagereit
Damien Fay

University of Koblenz–Landau, Germany
University College Cork, Ireland

konect.uni-koblenz.de

            Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   24
Questions
Did you try the power law exponent instead of the Gini coefficient?
    → Yes, but see (Kunegis & Preusse 2012)

Did you try the absolute value instead of the square in rankF ?
    → Yes, it leads to the nuclear norm instead of the Frobenius
    norm

Isn't it hard to find a maximal directed 2-matching?
     → It takes a runtime of O(|V|1/2 |E|)

How is the approximation using only R eigenvalues for the WSD
justified?
     → By observing that all eigenvalues shrink


               Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   25
References
J. Kunegis, S. Sizov, F. Schwagereit, D. Fay. Diversity Dynamics in
Online Networks. Proc. Conf. on Hypertext and Social Media, 2012.

J. Kunegis, J. Preusse. Fairness on the Web: Alternatives to the Power
Law. Proc. Web Science Conf., 2012.

Y.-Y. Liu, J.-J. Slotine, A.-L. Barabási. Controllability of Complex
Networks. Nature, 473:167–173, May 2011.

J. Leskovec, J. Kleinberg, C. Faloutsos. Graph Evolution: Densification
and Shrinking Diameters. ACM Trans. Knowledge Discovery from Data,
1(1):1–40, 2007.

A.-L. Barabási, R. Albert. Emergence of Scaling in Random Networks.
Science, 286(5439):509–512, 1999.

                 Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   26
Credits

http://www.shewearsshortshorts.com/2012/01/downside.html
https://twitter.com/#!/justinbieber
http://www.iconspedia.com/icon/nerd-4255.html
http://hk.digikey.com/1/3/index1227.html




                Jérôme Kunegis et al.   Diversity Dynamics in Online Networks   27

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Diversity Dynamics in Online Networks (HT'2012)

  • 1. Web Science and Technologies University of Koblenz–Landau, Germany Diversity Dynamics in Online Networks Jérôme Kunegis¹ Sergej Sizov¹ Felix Schwagereit¹ Damien Fay² ¹ University of Koblenz–Landau, Germany ² University College Cork, Ireland HT 2012, Milwaukee, WI June 27, 2012
  • 2. Everyone likes good things: Jérôme Kunegis et al. Diversity Dynamics in Online Networks 2
  • 3. Or even better: Diversity! Jérôme Kunegis et al. Diversity Dynamics in Online Networks 3
  • 4. Structural Diversity Jérôme Kunegis et al. Diversity Dynamics in Online Networks 4
  • 5. (1) Length of paths Diversity No diversity “Large” world Small world Jérôme Kunegis et al. Diversity Dynamics in Online Networks 5
  • 6. 90-percentile effective diameter ±0.9 Hop plot Jérôme Kunegis et al. Diversity Dynamics in Online Networks 6
  • 7. “T he Wo rld Ge ts Sm a lle r” (Leskovec, Kleinberg & Faloutsos 2007) Jérôme Kunegis et al. Diversity Dynamics in Online Networks 7
  • 8. Outline (A) How can structural diversity be measured? (B) How does diversity change? Jérôme Kunegis et al. Diversity Dynamics in Online Networks 8
  • 9. (A) How to Measure Diversity in a Network? (1) Length of paths (2) Numbers of neighbors (3) Size of communities (4) Random walks (5) Controllability Jérôme Kunegis et al. Diversity Dynamics in Online Networks 9
  • 10. (2) Number of neighbors Diversity No diversity d(i) ¼ d(j) d(i) ¿ d(j) Jérôme Kunegis et al. Diversity Dynamics in Online Networks 10
  • 11. Gini Coefficient Jérôme Kunegis et al. Diversity Dynamics in Online Networks 11
  • 12. “The Rich Get Richer” (Barabási & Albert 1999) Jérôme Kunegis et al. Diversity Dynamics in Online Networks 12
  • 13. (3) Size of communities Diversity No diversity Jérôme Kunegis et al. Diversity Dynamics in Online Networks 13
  • 14. Fractional Rank Spectrum of the graph = f¸1, ¸2, ¸3, . . .g rankF = §k (¸k / ¸1) 2 = (kAkF / kAk2)2 Jérôme Kunegis et al. Diversity Dynamics in Online Networks 14
  • 15. “Eigenvector Preferential Attachment” Ui1 Uj1 > ¸1 / 2jEj Jérôme Kunegis et al. Diversity Dynamics in Online Networks 15
  • 16. (4) Random walks Diversity No diversity Pret(L) large Pret(L) small Jérôme Kunegis et al. Diversity Dynamics in Online Networks 16
  • 17. Weighted Spectral Distribution Pret(L) = §(i, j, . . . k) (d(i) d(j) . . . d(k)){1 = tr(NL) = § k ¸k L where ¸k are eigenvalues of N = D{1/2 A D{1/2. Here: Use L = 4 and k · R Jérôme Kunegis et al. Diversity Dynamics in Online Networks 17
  • 18. Eigenvalues of N Jérôme Kunegis et al. Diversity Dynamics in Online Networks 18
  • 19. “R an do m Wa lks Ar riv eL es sO ft e n” Jérôme Kunegis et al. Diversity Dynamics in Online Networks 19
  • 20. (5) Controllability Diversity No diversity (Liu, Slotine & Barabási 2011) Jérôme Kunegis et al. Diversity Dynamics in Online Networks 20
  • 21. Find a maximal directed 2-matching #Knobs needed = jVj { max jMj  Jérôme Kunegis et al. Diversity Dynamics in Online Networks 21
  • 22. “Ne two rks Get E as ier to C ont rol” Jérôme Kunegis et al. Diversity Dynamics in Online Networks 22
  • 23. (B) Experiments 20 networks from konect.uni-koblenz.de 9 authorship, 3 communication, 3 social, 3 interaction, 1 rating, 1 physical Measure Diversity No diversity Diversity decreasing trend increasing (1) Diameter 12 8 0 (2) Gini coefficient 13 3 5 (3) Fractional rank 10 6 4 (4) Weighted spectral distribution 12 7 1 (5) Controllability 15 5 0 Jérôme Kunegis et al. Diversity Dynamics in Online Networks 23
  • 24. Thank You Jérôme Kunegis @kunegis Sergej Sizov Felix Schwagereit Damien Fay University of Koblenz–Landau, Germany University College Cork, Ireland konect.uni-koblenz.de Jérôme Kunegis et al. Diversity Dynamics in Online Networks 24
  • 25. Questions Did you try the power law exponent instead of the Gini coefficient? → Yes, but see (Kunegis & Preusse 2012) Did you try the absolute value instead of the square in rankF ? → Yes, it leads to the nuclear norm instead of the Frobenius norm Isn't it hard to find a maximal directed 2-matching? → It takes a runtime of O(|V|1/2 |E|) How is the approximation using only R eigenvalues for the WSD justified? → By observing that all eigenvalues shrink Jérôme Kunegis et al. Diversity Dynamics in Online Networks 25
  • 26. References J. Kunegis, S. Sizov, F. Schwagereit, D. Fay. Diversity Dynamics in Online Networks. Proc. Conf. on Hypertext and Social Media, 2012. J. Kunegis, J. Preusse. Fairness on the Web: Alternatives to the Power Law. Proc. Web Science Conf., 2012. Y.-Y. Liu, J.-J. Slotine, A.-L. Barabási. Controllability of Complex Networks. Nature, 473:167–173, May 2011. J. Leskovec, J. Kleinberg, C. Faloutsos. Graph Evolution: Densification and Shrinking Diameters. ACM Trans. Knowledge Discovery from Data, 1(1):1–40, 2007. A.-L. Barabási, R. Albert. Emergence of Scaling in Random Networks. Science, 286(5439):509–512, 1999. Jérôme Kunegis et al. Diversity Dynamics in Online Networks 26