One more edge case-test+fix

martinmodrak · martinmodrak · commit 6aed316f5f8e · 2020-03-12T12:25:02.000+01:00
diff --git a/stan/math/prim/fun/binomial_coefficient_log.hpp b/stan/math/prim/fun/binomial_coefficient_log.hpp
@@ -84,7 +84,7 @@ inline return_type_t<T_n, T_k> binomial_coefficient_log(const T_n n,
   }
 
   // Choosing the more stable of the symmetric branches
-  if (n > 0 && k > value_of_rec(n) / 2.0 + 1e-8) {
+  if (n > -1 && k > value_of_rec(n) / 2.0 + 1e-8) {
     return binomial_coefficient_log(n, n - k);
   }
 
diff --git a/test/unit/math/rev/fun/binomial_coefficient_log_test.cpp b/test/unit/math/rev/fun/binomial_coefficient_log_test.cpp
@@ -106,6 +106,8 @@ std::vector<TestValue> testValuesEdge = {
     {3, -1, stan::math::NEGATIVE_INFTY, -0.25, stan::math::INFTY},
     {-1, -0.2, stan::math::INFTY, stan::math::NEGATIVE_INFTY,
      -4.324031329886049836},
+    {-0.5, 0.5, stan::math::NEGATIVE_INFTY, stan::math::INFTY,
+     stan::math::NEGATIVE_INFTY},
     {4.0, 5.0, stan::math::NEGATIVE_INFTY, stan::math::INFTY,
      stan::math::NEGATIVE_INFTY},
     {1, 0, 0, 0, 1},

Original file line number	Diff line number	Diff line change
`@@ -84,7 +84,7 @@ inline return_type_t<T_n, T_k> binomial_coefficient_log(const T_n n,`
`84`	`84`	`}`
`85`	`85`
`86`	`86`	`// Choosing the more stable of the symmetric branches`
`87`		`- if (n > 0 && k > value_of_rec(n) / 2.0 + 1e-8) {`
	`87`	`+ if (n > -1 && k > value_of_rec(n) / 2.0 + 1e-8) {`
`88`	`88`	`return binomial_coefficient_log(n, n - k);`
`89`	`89`	`}`
`90`	`90`