Add BitFlip and Sometimes Emission classes

cxx/emissions/BUILD

@@ -9,13 +9,51 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "bitflip",
+    srcs = ["bitflip.hh"],
+    visibility = ["//:__subpackages__"],
+    deps = [":base"],
+)
+
 cc_library(
     name = "gaussian",
     srcs = ["gaussian.hh"],
     visibility = ["//:__subpackages__"],
     deps = [":base"],
 )
 
+cc_library(
+    name = "sometimes",
+    srcs = ["sometimes.hh"],
+    visibility = ["//:__subpackages__"],
+    deps = [
+        ":base",
+        "//distributions:beta_bernoulli",
+    ],
+)
+
+cc_test(
+    name = "bitflip_test",
+    srcs = ["bitflip_test.cc"],
+    deps = [
+        ":bitflip",
+        "@boost//:algorithm",
+        "@boost//:test",
+    ],
+)
+
+cc_test(
+    name = "sometimes_test",
+    srcs = ["sometimes_test.cc"],
+    deps = [
+        ":bitflip",
+        ":sometimes",
+        "@boost//:algorithm",
+        "@boost//:test",
+    ],
+)
+
 # TODO(thomaswc): Fix and re-enable.
 #cc_test(
 #    name = "gaussian_test",

cxx/emissions/bitflip.hh

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <cassert>
+#include "emissions/base.hh"
+
+// A *deterministic* Emission class that always emits not(clean).
+// Most users will want to combine this with Sometimes.
+class BitFlip : public Emission<bool> {
+ public:
+  BitFlip() {};
+
+  void incorporate(const std::pair<bool, bool>& x) {
+    assert(x.first != x.second);
+    ++N;
+  }
+
+  void unincorporate(const std::pair<bool, bool>& x) {
+    assert(x.first != x.second);
+    --N;
+  }
+
+  double logp(const std::pair<bool, bool>& x) const {
+    assert(x.first != x.second);
+    return 0.0;
+  }
+
+  double logp_score() const {
+    return 0.0;
+  }
+
+  // No hyperparameters to transition!
+  void transition_hyperparameters() {}
+
+  bool sample_corrupted(const bool& clean, std::mt19937* unused_prng) {
+    return !clean;
+  }
+
+  bool propose_clean(const std::vector<bool>& corrupted,
+                           std::mt19937* unused_prng) {
+    return !corrupted[0];
+  }
+};

cxx/emissions/bitflip_test.cc

@@ -0,0 +1,33 @@
+// Apache License, Version 2.0, refer to LICENSE.txt
+
+#define BOOST_TEST_MODULE test BitFlip
+
+#include <random>
+
+#include "emissions/bitflip.hh"
+
+#include <boost/test/included/unit_test.hpp>
+
+BOOST_AUTO_TEST_CASE(test_simple) {
+  BitFlip bf;
+
+  BOOST_TEST(bf.logp_score() == 0.0);
+  BOOST_TEST(bf.N == 0);
+  bf.incorporate(std::make_pair<bool, bool>(true, false));
+  BOOST_TEST(bf.logp_score() == 0.0);
+  BOOST_TEST(bf.N == 1);
+  bf.unincorporate(std::make_pair<bool, bool>(true, false));
+  BOOST_TEST(bf.logp_score() == 0.0);
+  BOOST_TEST(bf.N == 0);
+  bf.incorporate(std::make_pair<bool, bool>(false, true));
+  bf.incorporate(std::make_pair<bool, bool>(false, true));
+  BOOST_TEST(bf.logp_score() == 0.0);
+  BOOST_TEST(bf.N == 2);
+
+  BOOST_TEST(bf.logp(std::make_pair<bool, bool>(true, false)) == 0.0);
+
+  std::mt19937 prng;
+  BOOST_TEST(bf.sample_corrupted(false, &prng));
+
+  BOOST_TEST(bf.propose_clean({false, false, false}, &prng));
+}

cxx/emissions/sometimes.hh

@@ -0,0 +1,75 @@
+#pragma once
+
+#include <unordered_map>
+
+#include "distributions/beta_bernoulli.hh"
+#include "emissions/base.hh"
+
+// An Emission class that sometimes applies BaseEmissor and sometimes doesn't.
+// BaseEmissor must (1) of type Emission<SampleType> and (2) assign zero
+// probability to <clean, dirty> pairs with clean == dirty.  [For example,
+// BitFlip and Gaussian both satisfy #2].
+template <typename BaseEmissor, typename SampleType = double>
+class Sometimes : public Emission<SampleType> {
+ public:
+  BetaBernoulli bb;
+  BaseEmissor be;
+
+  Sometimes() : bb(nullptr) {};
+
+  void incorporate(const std::pair<SampleType, SampleType>& x) {
+    ++(this->N);
+    bb.incorporate(x.first != x.second);
+    if (x.first != x.second) {
+      be.incorporate(x);
+    }
+  }
+
+  void unincorporate(const std::pair<SampleType, SampleType>& x) {
+    --(this->N);
+    bb.unincorporate(x.first != x.second);
+    if (x.first != x.second) {
+      be.unincorporate(x);
+    }
+  }
+
+  double logp(const std::pair<SampleType, SampleType>& x) const {
+    return bb.logp(x.first != x.second) + be.logp(x);
+  }
+
+  double logp_score() const {
+    return bb.logp_score() + be.logp_score();
+  }
+
+  void transition_hyperparameters() {
+    be.transition_hyperparameters();
+    bb.transition_hyperparameters();
+  }
+
+  SampleType sample_corrupted(const SampleType& clean, std::mt19937* prng) {
+    bb.prng = prng;
+    if (bb.sample()) {
+      return be.sample_corrupted(clean, prng);
+    }
+    return clean;
+  }
+
+  SampleType propose_clean(const std::vector<SampleType>& corrupted,
+                           std::mt19937* prng) {
+    // We approximate the maximum likelihood estimate by taking the mode of
+    // corrupted.  The full solution would construct BaseEmissor and
+    // BetaBernoulli instances for each choice of clean and picking the
+    // clean with the lowest combined logp_score().
+    std::unordered_map<SampleType, int> counts;
+    SampleType mode;
+    int max_count = 0;
+    for (const SampleType& c: corrupted) {
+      ++counts[c];
+      if (counts[c] > max_count) {
+        max_count = counts[c];
+        mode = c;
+      }
+    }
+    return mode;
+  }
+};

cxx/emissions/sometimes_test.cc

@@ -0,0 +1,33 @@
+// Apache License, Version 2.0, refer to LICENSE.txt
+
+#define BOOST_TEST_MODULE test Sometimes
+
+#include <random>
+
+#include "emissions/bitflip.hh"
+#include "emissions/sometimes.hh"
+
+#include <boost/test/included/unit_test.hpp>
+
+BOOST_AUTO_TEST_CASE(test_simple) {
+  Sometimes<BitFlip, bool> sbf;
+
+  double orig_lp = sbf.logp_score();
+  BOOST_TEST(sbf.N == 0);
+  sbf.incorporate(std::make_pair<bool, bool>(true, false));
+  BOOST_TEST(sbf.logp_score() < 0.0);
+  BOOST_TEST(sbf.N == 1);
+  sbf.unincorporate(std::make_pair<bool, bool>(true, false));
+  BOOST_TEST(sbf.logp_score() == orig_lp);
+  BOOST_TEST(sbf.N == 0);
+
+  sbf.incorporate(std::make_pair<bool, bool>(false, true));
+  sbf.incorporate(std::make_pair<bool, bool>(false, true));
+  BOOST_TEST(sbf.logp_score() < 0.0);
+  BOOST_TEST(sbf.N == 2);
+
+  BOOST_TEST(sbf.logp(std::make_pair<bool, bool>(true, false)) < 0.0);
+
+  std::mt19937 prng;
+  BOOST_TEST(sbf.propose_clean({true, true, false}, &prng));
+}