7. Topics over Time Bag of Timestamps Modification of LDA (Beta distribution for continuous timestamps) Modification of LDA (Dirichlet-multinomial for discrete timestamps ) O(NK) time, O(N) space N: number of word tokens O((N+L)K) time, O(N+L) space L: sum of timestamp array lengths Non-Bayesian term in updating formula for Gibbs sampling Additional input parameter for timestamp array lengths