Failing test

Author: martinmodrak

test/unit/math/prim/fun/binomial_coefficient_log_test.cpp

@@ -1,3 +1,4 @@
+#include <test/unit/math/expect_near_rel.hpp>
 #include <stan/math/prim.hpp>
 #include <gtest/gtest.h>
 #include <cmath>
@@ -7,7 +8,8 @@ template <typename T_N, typename T_n>
 void test_binom_coefficient(const T_N& N, const T_n& n) {
   using stan::math::binomial_coefficient_log;
   EXPECT_FLOAT_EQ(lgamma(N + 1) - lgamma(n + 1) - lgamma(N - n + 1),
-                  binomial_coefficient_log(N, n));
+                  binomial_coefficient_log(N, n))
+      << "N = " << N << ", n = " << n;
 }
 
 TEST(MathFunctions, binomial_coefficient_log) {
@@ -19,6 +21,15 @@ TEST(MathFunctions, binomial_coefficient_log) {
 
   EXPECT_FLOAT_EQ(29979.16, binomial_coefficient_log(100000, 91116));
 
+  EXPECT_EQ(binomial_coefficient_log(-1, 0), 0);  // Needed for neg_binomial_2
+  EXPECT_EQ(binomial_coefficient_log(50, 0), 0);
+  EXPECT_EQ(binomial_coefficient_log(10000, 0), 0);
+
+  EXPECT_EQ(binomial_coefficient_log(10, 11),
+            -std::numeric_limits<double>::infinity());
+  EXPECT_EQ(binomial_coefficient_log(10, -1),
+            -std::numeric_limits<double>::infinity());
+
   for (int n = 0; n < 1010; ++n) {
     test_binom_coefficient(1010, n);
     test_binom_coefficient(1010.0, n);
@@ -38,3 +49,55 @@ TEST(MathFunctions, binomial_coefficient_log_nan) {
   EXPECT_TRUE(std::isnan(stan::math::binomial_coefficient_log(nan, 2.0)));
   EXPECT_TRUE(std::isnan(stan::math::binomial_coefficient_log(nan, nan)));
 }
+
+TEST(MathFunctions, binomial_coefficient_log_errors_edge_cases) {
+  using stan::math::binomial_coefficient_log;
+  double inf = std::numeric_limits<double>::infinity();
+  EXPECT_NO_THROW(binomial_coefficient_log(10, 11));
+  EXPECT_THROW(binomial_coefficient_log(10, 11.01), std::domain_error);
+  EXPECT_THROW(binomial_coefficient_log(10, -1.1), std::domain_error);
+  EXPECT_THROW(binomial_coefficient_log(-1, 0.3), std::domain_error);
+  EXPECT_NO_THROW(binomial_coefficient_log(-0.5, 0.49));
+  EXPECT_NO_THROW(binomial_coefficient_log(10, -0.9));
+
+  EXPECT_FLOAT_EQ(binomial_coefficient_log(0, -1), -inf);
+  EXPECT_FLOAT_EQ(binomial_coefficient_log(-1, 0), 0);
+  EXPECT_FLOAT_EQ(binomial_coefficient_log(-1, -0.3), inf);
+  EXPECT_FLOAT_EQ(binomial_coefficient_log(0.3, -1), -inf);
+
+}
+
+namespace binomial_coefficient_test_internal {
+struct TestValue {
+  double n;
+  double k;
+  double val;
+};
+
+std::vector<TestValue> testValues = {  {-0.1,-0.9,-2.1152525390850903},  {-0.1,-1.0000000000000001e-11,1.7771062399418724e-12},  {-0.1,-1.0000000000000002e-6,1.7770950132278696e-7},  {-0.1,-0.001,0.00017592768030333383},  {-0.1,-0.020000000000000004,0.0028416866729211523},  {-0.1,-0.05,0.0044386492587971844},  {-0.1,-0.097,0.0005170837568402953},  {-0.1,-0.09999999400000001,1.0662676433991578e-9},  {-0.1,-0.09999999970000001,5.331331690149795e-11},  {-0.1,0.8,-2.1152525390850907},  {0.00003,-0.9,-2.21375637737528044964112},  {0.00003,3.e-15,1.48040820535563428588846e-19},  {0.00003,3.e-10,1.48039340142161568666212e-14},  {0.00003,3.e-7,1.46560412344434242311062e-11},  {0.00003,6.e-6,2.36865312869367134774661e-10},  {0.00003,0.000015,3.70102051348524044535716e-10},  {0.00003,0.0000291,4.30798787797857754693695e-11},  {0.00003,0.0000299999982,8.88244870007509649977929e-17},  {0.00003,0.00002999999991,4.44122460318735146597007e-18},  {0.00003,0.90003,-2.21375637737528044964112},  {0.002,-0.9,-2.21559326412971099686943},  {0.002,2.e-13,6.57013709556564677684856e-16},  {0.002,2.e-8,6.57007139476544583161173e-11},  {0.002,0.00002,6.50443564072189575550994e-8},  {0.002,0.0004,1.05122171458287350859763e-6},  {0.002,0.001,1.64253373496215313253469e-6},  {0.002,0.00194,1.91190982195918976356429e-7},  {0.002,0.00199999988,3.94208202120835082737684e-13},  {0.002,0.001999999994,1.97104112295366725515452e-14},  {0.002,0.902,-2.21559326412971099686943},  {1,-0.9,-2.85558226198351740582195},  {1,1.e-10,9.9999999988550659331851e-11},  {1,0.00001,9.99988550692664559909352e-6},  {1,0.01,0.00988583703486131052627978},  {1,0.2,0.156457962917688016707705},  {1,0.5,0.241564475270490444691037},  {1,0.97,0.028978328236256312960776},  {1,0.99999994,5.99999958782374313463811e-8},  {1,0.999999997,2.99999998969559340736596e-9},  {1,1.9,-2.85558226198351740582195},  {8,-0.9,-4.22528965320883461943031},  {8,8.e-10,2.17428571372173153982474e-9},  {8,0.00008,0.000217422931805073420417006},  {8,0.08,0.211982267378255838975509},  {8,1.6,2.90678606291134283426263},  {8,4,4.24849524204935898912334},  {8,7.76,0.606274586245453651115361},  {8,7.99999952,1.30457122553768403613331e-6},  {8,7.999999976,6.52285709209869625945566e-8},  {8,8.9,-4.22528965320883461943031},  {1325,-0.9,-8.72360867216657209762532},  {1325,1.325e-7,1.02909578020477960435539e-6},  {1325,0.01325,0.102766042691370430370992},  {1325,13.25,71.9898321274090629975055},  {1325,265,659.435649329029419323398},  {1325,662.5,914.599450340845275100724},  {1325,1285.25,175.786260651191862665015},  {1325,1324.9999205,0.000617452276410452190170437},  {1325,1324.999996025,0.0000308728608380968862741097},  {1325,1325.9,-8.72360867216657209762532},  {845000,-0.9,-14.5350963792733464918229},  {845000,0.0000845,0.00120194816738712136581358},  {845000,8.45,103.738303827736743600251},  {845000,8450,47315.8616457576200611209},  {845000,169000,422833.221695496506553128},  {845000,422500,585702.318235552114086514},  {845000,819650,113851.158132678562120685},  {845000,844999.9493,0.719108776819481762797449},  {845000,844999.997465,0.036053342347290003917417},  {845000,845000.9,-14.5350963792733464918229},  {3000000000000000.0,3,105.120406581508328854183},  {3000000000000000.0,100,3199.99949280231435502243},  {3000000000000000.0,12895,350387.5243605883687667},  {100000000000000000000.0,3,136.363346110414686040237},  {100000000000000000000.0,100,4241.4308104325278778424},  {100000000000000000000.0,12895,484680.092769031900296878},};
+}  // namespace binomial_coefficient_test_internal
+
+TEST(MathFunctions, binomial_coefficient_log_precomputed) {
+  using binomial_coefficient_test_internal::TestValue;
+  using binomial_coefficient_test_internal::testValues;
+  using stan::test::expect_near_rel;
+
+  for (TestValue t : testValues) {
+    std::ostringstream msg;
+    msg << std::setprecision(22) << "n = " << t.n << ", k = " << t.k;
+
+    double val = stan::math::binomial_coefficient_log(t.n, t.k);
+    expect_near_rel(msg.str(), val, t.val);
+
+    if (t.k > t.n / 10) {
+      // Testing the mirrored binomial coefficient is not performed for
+      // small k, as we may loose so much precision computing k2
+      // that the test becomes invalid
+      std::ostringstream msg2;
+      double k2 = t.n - t.k;
+      msg2 << std::setprecision(22) << "n = " << t.n << ", k = " << k2;
+      double val2 = stan::math::binomial_coefficient_log(t.n, k2);
+      expect_near_rel(msg2.str(), val2, t.val);
+    }
+  }
+}