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authorChris Dyer <cdyer@cs.cmu.edu>2012-03-10 00:00:27 -0500
committerChris Dyer <cdyer@cs.cmu.edu>2012-03-10 00:00:27 -0500
commite320dd47380f8f3a628073f926a56e4321146ebd (patch)
tree96ec890941ba80f02400292b11972a884276600b
parentef614a1d968aebbf463ed57876fee395b4c24635 (diff)
use quasi model 2 instead of uniform alignments
-rw-r--r--gi/pf/align-lexonly-pyp.cc6
-rw-r--r--gi/pf/quasi_model2.h46
2 files changed, 52 insertions, 0 deletions
diff --git a/gi/pf/align-lexonly-pyp.cc b/gi/pf/align-lexonly-pyp.cc
index 4a1d1db6..0c90b6ce 100644
--- a/gi/pf/align-lexonly-pyp.cc
+++ b/gi/pf/align-lexonly-pyp.cc
@@ -11,6 +11,7 @@
#include "sampler.h"
#include "corpus.h"
#include "pyp_tm.h"
+#include "quasi_model2.h"
using namespace std;
namespace po = boost::program_options;
@@ -61,12 +62,14 @@ struct Aligner {
Aligner(const vector<vector<WordID> >& lets, int num_letters, vector<AlignedSentencePair>* c) :
corpus(*c),
model(lets, num_letters),
+ paj(4, 0.08),
kNULL(TD::Convert("NULL")) {
assert(lets[kNULL].size() == 0);
}
vector<AlignedSentencePair>& corpus;
PYPLexicalTranslation model;
+ const QuasiModel2 paj;
const WordID kNULL;
void ResampleHyperparameters() {
@@ -83,6 +86,7 @@ struct Aligner {
a_j = prng->next() * (1 + asp.src.size());
const WordID f_a_j = (a_j ? asp.src[a_j - 1] : kNULL);
model.Increment(f_a_j, asp.trg[j], &*prng);
+ // TODO factor in alignment prob
}
}
cerr << "Corpus intialized randomly. LLH = " << model.Likelihood() << endl;
@@ -101,6 +105,8 @@ struct Aligner {
for (unsigned prop_a_j = 0; prop_a_j <= asp.src.size(); ++prop_a_j) {
const WordID prop_f = (prop_a_j ? asp.src[prop_a_j - 1] : kNULL);
ss[prop_a_j] = model.Prob(prop_f, e_j);
+ // TODO configurable
+ ss[prop_a_j] *= paj.Pa_j(prop_a_j, j, asp.src.size(), asp.trg.size());
}
a_j = prng->SelectSample(ss);
f_a_j = (a_j ? asp.src[a_j - 1] : kNULL);
diff --git a/gi/pf/quasi_model2.h b/gi/pf/quasi_model2.h
new file mode 100644
index 00000000..0095289f
--- /dev/null
+++ b/gi/pf/quasi_model2.h
@@ -0,0 +1,46 @@
+#ifndef _QUASI_MODEL2_H_
+#define _QUASI_MODEL2_H_
+
+#include <vector>
+#include <cmath>
+#include "prob.h"
+#include "array2d.h"
+
+struct QuasiModel2 {
+ explicit QuasiModel2(double alpha, double pnull = 0.1) :
+ alpha_(alpha),
+ pnull_(pnull),
+ pnotnull_(1 - pnull),
+ z_(1000,1000) {}
+ // a_j = 0 => NULL; src_len does *not* include null
+ prob_t Pa_j(unsigned a_j, unsigned j, unsigned src_len, unsigned trg_len) const {
+ if (!a_j) return pnull_;
+ std::vector<prob_t>& zv = z_(src_len, trg_len);
+ if (zv.size() == 0)
+ zv.resize(trg_len);
+
+ prob_t& z = zv[j];
+ if (z.is_0()) z = ComputeZ(j, src_len, trg_len);
+
+ prob_t p;
+ p.logeq(-fabs(double(a_j - 1) / src_len - double(j) / trg_len) * alpha_);
+ p *= pnotnull_;
+ p /= z;
+ return p;
+ }
+ private:
+ prob_t ComputeZ(unsigned j, unsigned src_len, unsigned trg_len) const {
+ prob_t p, z = prob_t::Zero();
+ for (int a_j = 1; a_j <= src_len; ++a_j) {
+ p.logeq(-fabs(double(a_j - 1) / src_len - double(j) / trg_len) * alpha_);
+ z += p;
+ }
+ return z;
+ }
+ double alpha_;
+ const prob_t pnull_;
+ const prob_t pnotnull_;
+ mutable Array2D<std::vector<prob_t> > z_;
+};
+
+#endif