dpmm-gmm

Dirichlet Process Mixtures for Generalized Mallows Models Efficient C/Matlab MCMC sampling for Dirichlet Process Mixtures of Generalized Mallows Models described in

Marina Meila and Harr Chen "Bayesian non-parametric clustering of ranking data" IEEE-TPAMI, to appear 2015

Please cite the paper if you are using this code.

Authors: Harr Chen harr@gmail.com Marina Meila mmp@stat.washington.edu

Generalities

v4/     the Slice-Gibbs and Beta-Gibbs sampler
exact/  the Exact-Beta-Gibbs sampler

Beta-Gibbs

is fast and exact for top-t rankings where t < n-10, n being the length of a complete permutation. For t closer to n, Beta-Gibbs is an approximate sampler

Exact-Beta-Gibbs

is an exact sampler for the cases when Beta-Gibbs is not, when the parameter t0 is large enough. Experimentally, we found t0 = 11 to be sufficient.

Exact-Beta-Gibbs is much slower than Beta-Gibbs, sometimes even slower than Slice-Gibbs. This is measured per iteration. But mixing is much better than for Slice-Gibbs, so it should require fewer iterations.

Slice-Gibbs

is exact, slower in time per iteration, slower mixing. Not really recommended in any situation. Was introduced as the "straw-man" for the other two.

Set up

1. download the code (v4 or exact)

2. compile

   mex -largeArrayDims sample_model.c mex -largeArrayDims compute_pi_R.c

for exact replace sample_model.c with sample_model_t0.c

To eke a bit more performance do:

mex -largeArrayDims -v CFLAGS='$CFLAGS -O4 -mtune=native -march=native -pipe -ffast-math -mfpmath=sse -msse4 -m64 -ansi -D_GNU_SOURCE -fexceptions -fPIC -fno-omit-frame-pointer -pthread' sample_model.c

3. choose running parameters

   define.h --> make numbers larger to see less test

4. call the code

The main entry point function for the sampler is inference.m. The comments should describe basically how to run it, but there's also an example script small_test.m that shows a very simple toy example.

Note: the permutations in this system are 0-based, not 1-based the theta parameters from the paper are denoted rho

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Bug reports by mmp:

1. only in exact, t0 should NOT be larger than tmax, or memory overflows will occur in resample_rho_beta_t0 and possibly other places.

2. resample_sigma_rho_t0 (inherited from resample_sigma_rho)

rho is sampled up to g_max_t in every cluster, even if in that cluster none of the data have length g_max_t. Haven't explored the consequences yet. If g_S[ idx+i ] is defined and 0 for the extra ranks, nothing drastic will happen, as rho will be sampled from the prior. But the extra rho's will affect the sampling of sigma

v4

Bug report by mmp: sample_model.c, around line 400, where *randLengthValue is calculated. I think that for BETA_SLICE g_sigma_gibbs should be g_rho_slices