unigram pyp lm added

2 files changed, 215 insertions, 0 deletions

diff --git a/utils/alias_sampler.h b/utils/alias_sampler.h
new file mode 100644
index 00000000..85da9944
--- /dev/null
+++ b/utils/alias_sampler.h
@@ -0,0 +1,47 @@
+#ifndef _ALIAS_SAMPLER_H_
+#define _ALIAS_SAMPLER_H_
+
+#include <vector>
+#include <limits>
+
+// R. A. Kronmal and A. V. Peterson, Jr. (1977) On the alias method for
+// generating random variables from a discrete distribution. In The American
+// Statistician, Vol. 33, No. 4. Pages 214--218.
+//
+// Intuition: a multinomial with N outcomes can be rewritten as a uniform
+// mixture of N Bernoulli distributions. The ith Bernoulli returns i with
+// probability F[i], otherwise it returns an "alias" value L[i]. The
+// constructor computes the F's and L's given an arbitrary multionimial p in
+// O(n) time and Draw returns samples in O(1) time.
+struct AliasSampler {
+  explicit AliasSampler(const std::vector<double>& p) :
+      cutoffs_(p.size()),
+      aliases_(p.size(), std::numeric_limits<unsigned>::max()) {
+    const unsigned N = p.size();
+    std::vector<unsigned> s,g;
+    for (unsigned i = 0; i < N; ++i) {
+      const double cutoff = cutoffs_[i] = N * p[i];
+      if (cutoff >= 1.0) g.push_back(i); else s.push_back(i);
+    }
+    while(!s.empty() && !g.empty()) {
+      const unsigned k = g.back();
+      const unsigned j = s.back();
+      aliases_[j] = k;
+      cutoffs_[k] -= 1.0 - cutoffs_[j];
+      s.pop_back();
+      if (cutoffs_[k] < 1.0) {
+        g.pop_back();
+        s.push_back(k);
+      }
+    }
+  }
+  template <typename Uniform01Generator>
+  unsigned Draw(Uniform01Generator& u01) const {
+    const unsigned n = u01() * cutoffs_.size();
+    if (u01() > cutoffs_[n]) return aliases_[n]; else return n;
+  }
+  std::vector<double> cutoffs_;    // F
+  std::vector<unsigned> aliases_;  // L
+};
+
+#endif
diff --git a/utils/unigram_pyp_lm.cc b/utils/unigram_pyp_lm.cc
new file mode 100644
index 00000000..510e8839
--- /dev/null
+++ b/utils/unigram_pyp_lm.cc
@@ -0,0 +1,168 @@
+#include <iostream>
+#include <tr1/memory>
+#include <queue>
+
+#include <boost/functional.hpp>
+#include <boost/program_options.hpp>
+#include <boost/program_options/variables_map.hpp>
+
+#include "corpus_tools.h"
+#include "m.h"
+#include "tdict.h"
+#include "sampler.h"
+#include "ccrp.h"
+
+// A not very memory-efficient implementation of an 1-gram LM based on PYPs
+// as described in Y.-W. Teh. (2006) A Hierarchical Bayesian Language Model
+// based on Pitman-Yor Processes. In Proc. ACL.
+
+using namespace std;
+using namespace tr1;
+namespace po = boost::program_options;
+
+boost::shared_ptr<MT19937> prng;
+
+void InitCommandLine(int argc, char** argv, po::variables_map* conf) {
+  po::options_description opts("Configuration options");
+  opts.add_options()
+        ("samples,n",po::value<unsigned>()->default_value(50),"Number of samples")
+        ("train,i",po::value<string>(),"Training data file")
+        ("test,T",po::value<string>(),"Test data file")
+        ("discount_prior_a,a",po::value<double>()->default_value(1.0), "discount ~ Beta(a,b): a=this")
+        ("discount_prior_b,b",po::value<double>()->default_value(1.0), "discount ~ Beta(a,b): b=this")
+        ("strength_prior_s,s",po::value<double>()->default_value(1.0), "strength ~ Gamma(s,r): s=this")
+        ("strength_prior_r,r",po::value<double>()->default_value(1.0), "strength ~ Gamma(s,r): r=this")
+        ("random_seed,S",po::value<uint32_t>(), "Random seed");
+  po::options_description clo("Command line options");
+  clo.add_options()
+        ("config", po::value<string>(), "Configuration file")
+        ("help", "Print this help message and exit");
+  po::options_description dconfig_options, dcmdline_options;
+  dconfig_options.add(opts);
+  dcmdline_options.add(opts).add(clo);
+  
+  po::store(parse_command_line(argc, argv, dcmdline_options), *conf);
+  if (conf->count("config")) {
+    ifstream config((*conf)["config"].as<string>().c_str());
+    po::store(po::parse_config_file(config, dconfig_options), *conf);
+  }
+  po::notify(*conf);
+
+  if (conf->count("help") || (conf->count("train") == 0)) {
+    cerr << dcmdline_options << endl;
+    exit(1);
+  }
+}
+
+// uniform base distribution (0-gram model)
+struct UniformWordModel {
+  explicit UniformWordModel(unsigned vocab_size) : p0(1.0 / vocab_size), draws() {}
+  void increment() { ++draws; }
+  void decrement() { --draws; assert(draws >= 0); }
+  double prob(WordID) const { return p0; } // all words have equal prob
+  double log_likelihood() const { return draws * log(p0); }
+  const double p0;
+  int draws;
+};
+
+// represents an Unigram LM
+struct UnigramLM {
+  UnigramLM(unsigned vs, double da, double db, double ss, double sr) :
+      uniform_vocab(vs),
+      crp(da, db, ss, sr, 0.8, 1.0) {}
+  void increment(WordID w, MT19937* rng) {
+    const double backoff = uniform_vocab.prob(w);
+    if (crp.increment(w, backoff, rng))
+      uniform_vocab.increment();
+  }
+  void decrement(WordID w, MT19937* rng) {
+    if (crp.decrement(w, rng))
+      uniform_vocab.decrement();
+  }
+  double prob(WordID w) const {
+    const double backoff = uniform_vocab.prob(w);
+    return crp.prob(w, backoff);
+  }
+
+  double log_likelihood() const {
+    double llh = uniform_vocab.log_likelihood();
+    llh += crp.log_crp_prob();
+    return llh;
+  }
+
+  void resample_hyperparameters(MT19937* rng) {
+    crp.resample_hyperparameters(rng);
+  }
+
+  double discount_a, discount_b, strength_s, strength_r;
+  double d, strength;
+  UniformWordModel uniform_vocab;
+  CCRP<WordID> crp;
+};
+
+int main(int argc, char** argv) {
+  po::variables_map conf;
+
+  InitCommandLine(argc, argv, &conf);
+  const unsigned samples = conf["samples"].as<unsigned>();
+  if (conf.count("random_seed"))
+    prng.reset(new MT19937(conf["random_seed"].as<uint32_t>()));
+  else
+    prng.reset(new MT19937);
+  MT19937& rng = *prng;
+  vector<vector<WordID> > corpuse;
+  set<WordID> vocabe;
+  const WordID kEOS = TD::Convert("</s>");
+  cerr << "Reading corpus...\n";
+  CorpusTools::ReadFromFile(conf["train"].as<string>(), &corpuse, &vocabe);
+  cerr << "E-corpus size: " << corpuse.size() << " sentences\t (" << vocabe.size() << " word types)\n";
+  vector<vector<WordID> > test;
+  if (conf.count("test"))
+    CorpusTools::ReadFromFile(conf["test"].as<string>(), &test);
+  else
+    test = corpuse;
+  UnigramLM lm(vocabe.size(),
+               conf["discount_prior_a"].as<double>(),
+               conf["discount_prior_b"].as<double>(),
+               conf["strength_prior_s"].as<double>(),
+               conf["strength_prior_r"].as<double>());
+  for (int SS=0; SS < samples; ++SS) {
+    for (int ci = 0; ci < corpuse.size(); ++ci) {
+      const vector<WordID>& s = corpuse[ci];
+      for (int i = 0; i <= s.size(); ++i) {
+        WordID w = (i < s.size() ? s[i] : kEOS);
+        if (SS > 0) lm.decrement(w, &rng);
+        lm.increment(w, &rng);
+      }
+      if (SS > 0) lm.decrement(kEOS, &rng);
+      lm.increment(kEOS, &rng);
+    }
+    cerr << "LLH=" << lm.log_likelihood() << endl;
+    //if (SS % 10 == 9) lm.resample_hyperparameters(&rng);
+  }
+  double llh = 0;
+  unsigned cnt = 0;
+  unsigned oovs = 0;
+  for (int ci = 0; ci < test.size(); ++ci) {
+    const vector<WordID>& s = test[ci];
+    for (int i = 0; i <= s.size(); ++i) {
+      WordID w = (i < s.size() ? s[i] : kEOS);
+      double lp = log(lm.prob(w)) / log(2);
+      if (i < s.size() && vocabe.count(w) == 0) {
+        cerr << "**OOV ";
+        ++oovs;
+        lp = 0;
+      }
+      cerr << "p(" << TD::Convert(w) << ") = " << lp << endl;
+      llh -= lp;
+      cnt++;
+    }
+  }
+  cerr << "  Log_10 prob: " << (-llh * log(2) / log(10)) << endl;
+  cerr << "        Count: " << cnt << endl;
+  cerr << "         OOVs: " << oovs << endl;
+  cerr << "Cross-entropy: " << (llh / cnt) << endl;
+  cerr << "   Perplexity: " << pow(2, llh / cnt) << endl;
+  return 0;
+}
+