From 8e60188039211c9a585625dd8309f2ba57b0cbb2 Mon Sep 17 00:00:00 2001
From: Chris Dyer <redpony@gmail.com>
Date: Tue, 18 Mar 2014 01:41:17 -0400
Subject: star function

---
 decoder/Makefile.am    |  1 -
 decoder/exp_semiring.h | 71 --------------------------------------------------
 decoder/hg.h           | 17 +++++++++++-
 utils/Makefile.am      |  2 ++
 utils/exp_semiring.h   | 64 +++++++++++++++++++++++++++++++++++++++++++++
 utils/logval.h         | 12 +++++++++
 utils/star.h           | 12 +++++++++
 7 files changed, 106 insertions(+), 73 deletions(-)
 delete mode 100644 decoder/exp_semiring.h
 create mode 100644 utils/exp_semiring.h
 create mode 100644 utils/star.h

diff --git a/decoder/Makefile.am b/decoder/Makefile.am
index c41cd7f9..7481192b 100644
--- a/decoder/Makefile.am
+++ b/decoder/Makefile.am
@@ -37,7 +37,6 @@ libcdec_a_SOURCES = \
   csplit.h \
   decoder.h \
   earley_composer.h \
-  exp_semiring.h \
   factored_lexicon_helper.h \
   ff.h \
   ff_basic.h \
diff --git a/decoder/exp_semiring.h b/decoder/exp_semiring.h
deleted file mode 100644
index 2a9034bb..00000000
--- a/decoder/exp_semiring.h
+++ /dev/null
@@ -1,71 +0,0 @@
-#ifndef _EXP_SEMIRING_H_
-#define _EXP_SEMIRING_H_
-
-#include <iostream>
-
-// this file implements the first-order expectation semiring described
-// in Li & Eisner (EMNLP 2009)
-
-// requirements:
-//   RType * RType ==> RType
-//   PType * PType ==> PType
-//   RType * PType ==> RType
-// good examples:
-//   PType scalar, RType vector
-// BAD examples:
-//   PType vector, RType scalar
-template <class PType, class RType>
-struct PRPair {
-  PRPair() : p(), r() {}
-  // Inside algorithm requires that T(0) and T(1)
-  // return the 0 and 1 values of the semiring
-  explicit PRPair(double x) : p(x), r() {}
-  PRPair(const PType& p, const RType& r) : p(p), r(r) {}
-  PRPair& operator+=(const PRPair& o) {
-    p += o.p;
-    r += o.r;
-    return *this;
-  }
-  PRPair& operator*=(const PRPair& o) {
-    r = (o.r * p) + (o.p * r);
-    p *= o.p;
-    return *this;
-  }
-  PType p;
-  RType r;
-};
-
-template <class P, class R>
-std::ostream& operator<<(std::ostream& o, const PRPair<P,R>& x) {
-  return o << '<' << x.p << ", " << x.r << '>';
-}
-
-template <class P, class R>
-const PRPair<P,R> operator+(const PRPair<P,R>& a, const PRPair<P,R>& b) {
-  PRPair<P,R> result = a;
-  result += b;
-  return result;
-}
-
-template <class P, class R>
-const PRPair<P,R> operator*(const PRPair<P,R>& a, const PRPair<P,R>& b) {
-  PRPair<P,R> result = a;
-  result *= b;
-  return result;
-}
-
-template <class P, class PWeightFunction, class R, class RWeightFunction>
-struct PRWeightFunction {
-  explicit PRWeightFunction(const PWeightFunction& pwf = PWeightFunction(),
-                            const RWeightFunction& rwf = RWeightFunction()) :
-    pweight(pwf), rweight(rwf) {}
-  PRPair<P,R> operator()(const HG::Edge& e) const {
-    const P p = pweight(e);
-    const R r = rweight(e);
-    return PRPair<P,R>(p, r * p);
-  }
-  const PWeightFunction pweight;
-  const RWeightFunction rweight;
-};
-
-#endif
diff --git a/decoder/hg.h b/decoder/hg.h
index 3d8cd9bc..343b99cf 100644
--- a/decoder/hg.h
+++ b/decoder/hg.h
@@ -25,6 +25,7 @@
 #include "tdict.h"
 #include "trule.h"
 #include "prob.h"
+#include "exp_semiring.h"
 #include "indices_after.h"
 #include "nt_span.h"
 
@@ -527,7 +528,21 @@ struct EdgeFeaturesAndProbWeightFunction {
 
 struct TransitionCountWeightFunction {
   typedef double Weight;
-  inline double operator()(const HG::Edge& e) const { (void)e; return 1.0; }
+  inline double operator()(const HG::Edge&) const { return 1.0; }
+};
+
+template <class P, class PWeightFunction, class R, class RWeightFunction>
+struct PRWeightFunction {
+  explicit PRWeightFunction(const PWeightFunction& pwf = PWeightFunction(),
+                            const RWeightFunction& rwf = RWeightFunction()) :
+    pweight(pwf), rweight(rwf) {}
+  PRPair<P,R> operator()(const HG::Edge& e) const {
+    const P p = pweight(e);
+    const R r = rweight(e);
+    return PRPair<P,R>(p, r * p);
+  }
+  const PWeightFunction pweight;
+  const RWeightFunction rweight;
 };
 
 #endif
diff --git a/utils/Makefile.am b/utils/Makefile.am
index a22b6727..c0ce3509 100644
--- a/utils/Makefile.am
+++ b/utils/Makefile.am
@@ -27,6 +27,7 @@ libutils_a_SOURCES = \
   citycrc.h \
   corpus_tools.h \
   dict.h \
+  exp_semiring.h \
   fast_sparse_vector.h \
   fdict.h \
   feature_vector.h \
@@ -49,6 +50,7 @@ libutils_a_SOURCES = \
   show.h \
   small_vector.h \
   sparse_vector.h \
+  star.h \
   static_utoa.h \
   stringlib.h \
   tdict.h \
diff --git a/utils/exp_semiring.h b/utils/exp_semiring.h
new file mode 100644
index 00000000..7572ccf5
--- /dev/null
+++ b/utils/exp_semiring.h
@@ -0,0 +1,64 @@
+#ifndef _EXP_SEMIRING_H_
+#define _EXP_SEMIRING_H_
+
+#include <iostream>
+#include "star.h"
+
+// this file implements the first-order expectation semiring described
+// in Li & Eisner (EMNLP 2009)
+
+// requirements:
+//   RType * RType ==> RType
+//   PType * PType ==> PType
+//   RType * PType ==> RType
+// good examples:
+//   PType scalar, RType vector
+// BAD examples:
+//   PType vector, RType scalar
+template <class PType, class RType>
+struct PRPair {
+  PRPair() : p(), r() {}
+  // Inside algorithm requires that T(0) and T(1)
+  // return the 0 and 1 values of the semiring
+  explicit PRPair(double x) : p(x), r() {}
+  PRPair(const PType& p, const RType& r) : p(p), r(r) {}
+  PRPair& operator+=(const PRPair& o) {
+    p += o.p;
+    r += o.r;
+    return *this;
+  }
+  PRPair& operator*=(const PRPair& o) {
+    r = (o.r * p) + (o.p * r);
+    p *= o.p;
+    return *this;
+  }
+  PType p;
+  RType r;
+};
+
+template <class P, class R>
+std::ostream& operator<<(std::ostream& o, const PRPair<P,R>& x) {
+  return o << '<' << x.p << ", " << x.r << '>';
+}
+
+template <class P, class R>
+const PRPair<P,R> operator+(const PRPair<P,R>& a, const PRPair<P,R>& b) {
+  PRPair<P,R> result = a;
+  result += b;
+  return result;
+}
+
+template <class P, class R>
+const PRPair<P,R> operator*(const PRPair<P,R>& a, const PRPair<P,R>& b) {
+  PRPair<P,R> result = a;
+  result *= b;
+  return result;
+}
+
+template <class P, class R>
+const PRPair<P,R> star(const PRPair<P,R>& x) {
+  const P pstar = star(x.p);
+  return PRPair<P,R>(pstar, pstar * x.r * pstar);
+}
+
+#endif
diff --git a/utils/logval.h b/utils/logval.h
index ec1f6acd..7f1e1024 100644
--- a/utils/logval.h
+++ b/utils/logval.h
@@ -11,6 +11,7 @@
 #include <cassert>
 #include "semiring.h"
 #include "show.h"
+#include "star.h"
 
 //TODO: template for supporting negation or not - most uses are for nonnegative "probs" only; probably some 10-20% speedup available
 template <class T>
@@ -242,4 +243,15 @@ bool operator>=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
 template <class T>
 std::size_t hash_value(const LogVal<T>& x) { return x.hash_impl(); }
 
+template <class T>
+LogVal<T> star(LogVal<T> x) {
+  if (x.is_0()) return x;
+  if (x.v_ >= 0) {
+    x.v_ = std::numeric_limits<T>::infinity();
+  } else {
+    x.v_ = -log1p(-x.as_float());
+  }
+  return x;
+}
+
 #endif
diff --git a/utils/star.h b/utils/star.h
new file mode 100644
index 00000000..3295112c
--- /dev/null
+++ b/utils/star.h
@@ -0,0 +1,12 @@
+#ifndef _STAR_H_
+#define _STAR_H_
+
+template <typename T>
+T star(const T& x) {
+  if (!x) return T();
+  if (x > T(1)) return std::numeric_limits<T>::infinity();
+  if (x < -T(1)) return -std::numeric_limits<T>::infinity();
+  return T(1) / (T(1) - x);
+}
+
+#endif
-- 
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