cdec --[prelm_]density_prune

git-svn-id: https://ws10smt.googlecode.com/svn/trunk@150 ec762483-ff6d-05da-a07a-a48fb63a330f

2 files changed, 55 insertions, 42 deletions

diff --git a/decoder/cdec.cc b/decoder/cdec.cc
index e3a2435d..bb29bafb 100644
--- a/decoder/cdec.cc
+++ b/decoder/cdec.cc
@@ -86,6 +86,8 @@ void InitCommandLine(int argc, char** argv, po::variables_map* conf) {
         ("show_expected_length", "Show the expected translation length under the model")
         ("show_partition,z", "Compute and show the partition (inside score)")
         ("show_cfg_search_space", "Show the search space as a CFG")
+    ("prelm_density_prune", po::value<double>(), "Applied to -LM forest just before final LM rescoring: keep no more than this many times the number of edges used in the best derivation tree (>=1.0)")
+    ("density_prune", po::value<double>(), "Keep no more than this many times the number of edges used in the best derivation tree (>=1.0)")
         ("prelm_beam_prune", po::value<double>(), "Prune paths from -LM forest before LM rescoring, keeping paths within exp(alpha>=0)")
         ("beam_prune", po::value<double>(), "Prune paths from +LM forest, keep paths within exp(alpha>=0)")
     ("scale_prune_srclen", "scale beams by the input length (in # of tokens; may not be what you want for lattices")
@@ -241,7 +243,7 @@ static void ExtractRulesDedupe(const Hypergraph& hg, ostream* os) {
 
 void register_feature_functions();
 
-bool beam_param(po::variables_map const& conf,char const* name,double *val,bool scale_srclen=false,double srclen=1)
+bool beam_param(po::variables_map const& conf,string const& name,double *val,bool scale_srclen=false,double srclen=1)
 {
   if (conf.count(name)) {
     *val=conf[name].as<double>()*(scale_srclen?srclen:1);
@@ -263,6 +265,28 @@ bool prelm_weights_string(po::variables_map const& conf,string &s)
   return false;
 }
 
+void maybe_prune(Hypergraph &forest,po::variables_map const& conf,string nbeam,string ndensity,string forestname,double srclen) {
+    double beam_prune,density_prune;
+    bool use_beam_prune=beam_param(conf,nbeam,&beam_prune,conf.count("scale_prune_srclen"),srclen);
+    bool use_density_prune=beam_param(conf,ndensity,&density_prune);
+    if (use_beam_prune || use_density_prune) {
+      double presize=forest.edges_.size();
+      vector<bool> preserve_mask,*pm=0;
+      if (conf.count("csplit_preserve_full_word")) {
+        preserve_mask.resize(forest.edges_.size());
+        preserve_mask[CompoundSplit::GetFullWordEdgeIndex(forest)] = true;
+        pm=&preserve_mask;
+      }
+      if (use_beam_prune)
+        forest.BeamPruneInsideOutside(1.0, false, beam_prune, pm);
+      if (use_density_prune)
+        forest.DensityPruneInsideOutside(1.0 ,false, density_prune, pm);
+      if (!forestname.empty()) forestname=" "+forestname;
+      cerr << viterbi_stats(forest,"  Pruned "+forestname+" forest",false,false);
+      cerr << "  Pruned "<<forestname<<" forest portion of edges kept: "<<forest.edges_.size()/presize<<endl;
+    }
+}
+
 
 int main(int argc, char** argv) {
   global_ff_registry.reset(new FFRegistry);
@@ -282,12 +306,11 @@ int main(int argc, char** argv) {
   const string formalism = LowercaseString(conf["formalism"].as<string>());
   const bool csplit_preserve_full_word = conf.count("csplit_preserve_full_word");
   if (csplit_preserve_full_word &&
-      (formalism != "csplit" || !conf.count("beam_prune"))) {
+      (formalism != "csplit" || !(conf.count("beam_prune")||conf.count("density_prune")||conf.count("prelm_beam_prune")||conf.count("prelm_density_prune")))) {
     cerr << "--csplit_preserve_full_word should only be "
-         << "used with csplit AND --beam_prune!\n";
+         << "used with csplit AND --*_prune!\n";
     exit(1);
   }
-  const bool scale_prune_srclen=conf.count("scale_prune_srclen");
   const bool csplit_output_plf = conf.count("csplit_output_plf");
   if (csplit_output_plf && formalism != "csplit") {
     cerr << "--csplit_output_plf should only be used with csplit!\n";
@@ -477,13 +500,7 @@ int main(int argc, char** argv) {
       cerr << viterbi_stats(forest," prelm forest",true,show_tree_structure);
     }
 
-    double prelm_beam_prune;
-    if (beam_param(conf,"prelm_beam_prune",&prelm_beam_prune,scale_prune_srclen,srclen)) {
-      double presize=forest.edges_.size();
-      forest.BeamPruneInsideOutside(1.0, false, prelm_beam_prune, NULL);
-      cerr << viterbi_stats(forest,"  Pruned -LM forest",false,false);
-      cerr << "  Pruned -LM forest (beam="<<prelm_beam_prune<<") portion of edges kept: "<<forest.edges_.size()/presize<<endl;
-    }
+    maybe_prune(forest,conf,"prelm_beam_prune","prelm_density_prune","-LM",srclen);
 
     bool has_late_models = !late_models.empty();
     if (has_late_models) {
@@ -501,14 +518,8 @@ int main(int argc, char** argv) {
       forest.Reweight(feature_weights);
       cerr << viterbi_stats(forest,"  +LM forest",true,show_tree_structure);
     }
-    double beam_prune;
-    if (beam_param(conf,"beam_prune",&beam_prune,scale_prune_srclen,srclen)) {
-      vector<bool> preserve_mask(forest.edges_.size(), false);
-      if (csplit_preserve_full_word)
-        preserve_mask[CompoundSplit::GetFullWordEdgeIndex(forest)] = true;
-      forest.BeamPruneInsideOutside(1.0, false, beam_prune, &preserve_mask);
-      cerr << viterbi_stats(forest,"  Pruned forest",false,false);
-    }
+
+    maybe_prune(forest,conf,"beam_prune","density_prune","+LM",srclen);
 
     if (conf.count("forest_output") && !has_ref) {
       ForestWriter writer(conf["forest_output"].as<string>(), sent_id);
diff --git a/decoder/hg.cc b/decoder/hg.cc
index 70511c07..11dd6f44 100644
--- a/decoder/hg.cc
+++ b/decoder/hg.cc
@@ -175,10 +175,31 @@ void Hypergraph::PruneEdges(const std::vector<bool>& prune_edge, bool run_inside
   TopologicallySortNodesAndEdges(nodes_.size() - 1, &filtered);
 }
 
+void Hypergraph_finish_prune(Hypergraph &hg,vector<prob_t> const& io,double cutoff,vector<bool> const* preserve_mask,bool verbose=false)
+{
+  vector<bool> prune(hg.NumberOfEdges());
+  if (verbose) {
+    if (preserve_mask) cerr << preserve_mask->size() << " " << prune.size() << endl;
+    cerr<<"Finishing prune for "<<prune.size()<<" edges; CUTOFF=" << cutoff << endl;
+  }
+  unsigned pc = 0;
+  for (int i = 0; i < io.size(); ++i) {
+    const bool prune_edge = (io[i] < cutoff);
+    if (prune_edge) {
+      ++pc;
+      prune[i] = !(preserve_mask && (*preserve_mask)[i]);
+    }
+  }
+  if (verbose)
+    cerr << "Finished pruning; removed " << pc << "/" << io.size() << " edges\n";
+  hg.PruneEdges(prune);
+}
+
 void Hypergraph::DensityPruneInsideOutside(const double scale,
                                            const bool use_sum_prod_semiring,
                                            const double density,
-                                           const vector<bool>* preserve_mask) {
+                                           const vector<bool>* preserve_mask)
+{
   assert(density >= 1.0);
   const int plen = ViterbiPathLength(*this);
   vector<WordID> bp;
@@ -195,13 +216,7 @@ void Hypergraph::DensityPruneInsideOutside(const double scale,
   assert(edges_.size() == io.size());
   vector<prob_t> sorted = io;
   nth_element(sorted.begin(), sorted.begin() + rnum, sorted.end(), greater<prob_t>());
-  const double cutoff = sorted[rnum];
-  vector<bool> prune(edges_.size());
-  for (int i = 0; i < edges_.size(); ++i) {
-    prune[i] = (io[i] < cutoff);
-    if (preserve_mask && (*preserve_mask)[i]) prune[i] = false;
-  }
-  PruneEdges(prune);
+  Hypergraph_finish_prune(*this,io,sorted[rnum],preserve_mask);
 }
 
 void Hypergraph::BeamPruneInsideOutside(
@@ -209,7 +224,7 @@ void Hypergraph::BeamPruneInsideOutside(
     const bool use_sum_prod_semiring,
     const double alpha,
     const vector<bool>* preserve_mask) {
-  assert(alpha >= 0.0);
+  assert(alpha > 0.0);
   assert(scale > 0.0);
   vector<prob_t> io(edges_.size());
   if (use_sum_prod_semiring)
@@ -220,20 +235,7 @@ void Hypergraph::BeamPruneInsideOutside(
   prob_t best;  // initializes to zero
   for (int i = 0; i < io.size(); ++i)
     if (io[i] > best) best = io[i];
-  const prob_t aprob(exp(-alpha));
-  const prob_t cutoff = best * aprob;
-  // cerr << "aprob = " << aprob << "\t  CUTOFF=" << cutoff << endl;
-  vector<bool> prune(edges_.size());
-  //cerr << preserve_mask.size() << " " << edges_.size() << endl;
-  int pc = 0;
-  for (int i = 0; i < io.size(); ++i) {
-    const bool prune_edge = (io[i] < cutoff);
-    if (prune_edge) ++pc;
-    prune[i] = (io[i] < cutoff);
-    if (preserve_mask && (*preserve_mask)[i]) prune[i] = false;
-  }
-  // cerr << "Beam pruning " << pc << "/" << io.size() << " edges\n";
-  PruneEdges(prune);
+  Hypergraph_finish_prune(*this,io,best*exp(-alpha),preserve_mask);
 }
 
 void Hypergraph::PrintGraphviz() const {