Incorrect domain restriction

Author: andrjohns

stan/math/prim/fun/hypergeometric_1F0.hpp

@@ -2,9 +2,10 @@
 #define STAN_MATH_PRIM_FUN_HYPERGEOMETRIC_1F0_HPP
 
 #include <stan/math/prim/meta.hpp>
+#include <stan/math/prim/err/check_less.hpp>
 #include <stan/math/prim/fun/boost_policy.hpp>
-#include <stan/math/prim/fun/floor.hpp>
 #include <boost/math/special_functions/hypergeometric_1F0.hpp>
+#include <cmath>
 
 namespace stan {
 namespace math {
@@ -28,16 +29,8 @@ namespace math {
  */
 template <typename Ta, typename Tz, require_all_arithmetic_t<Ta, Tz>* = nullptr>
 auto hypergeometric_1f0(const Ta& a, const Tz& z) {
-  bool condition_1 = z == 1.0;
-  bool condition_2 = (1.0 - z < 0.0) && floor(a) != a;
-  if (condition_1 || condition_2) {
-    std::stringstream msg;
-    msg << "Hypergeometric 1F0 is undefined when z == 1.0 or "
-        << "1 - z < 0 and a not an integer, but the following "
-        << "arguments provided: "
-        << "a: " << a << ", z: " << z << std::endl;
-    throw std::domain_error(msg.str());
-  }
+  constexpr const char* function = "hypergeometric_1f0";
+  check_less("hypergeometric_1f0", "abs(z)", std::abs(z), 1.0);
 
   return boost::math::hypergeometric_1F0(a, z, boost_policy_t<>());
 }

test/unit/math/mix/fun/hypergeometric_1F0_test.cpp

@@ -6,8 +6,10 @@ TEST(mathMixScalFun, hypergeometric_1f0) {
     return hypergeometric_1f0(x1, x2);
   };
 
-  stan::test::expect_ad(f, 0.5, 3.3);
+  stan::test::expect_ad(f, 5, 0.3);
   stan::test::expect_ad(f, 3.4, 0.9);
-  stan::test::expect_ad(f, 5.2, 6.7);
-  stan::test::expect_ad(f, 7.5, 1.8);
+  stan::test::expect_ad(f, 3.4, 0.1);
+  stan::test::expect_ad(f, 5, -0.7);
+  stan::test::expect_ad(f, 7, -0.1);
+  stan::test::expect_ad(f, 2.8, 0.8);
 }

test/unit/math/prim/fun/hypergeometric_1F0_test.cpp

@@ -7,15 +7,17 @@ TEST(MathFunctions, hypergeometric_1f0Double) {
   using stan::math::hypergeometric_1f0;
   using stan::math::inv;
 
-  EXPECT_FLOAT_EQ(-inv(27.0), hypergeometric_1f0(3, 4));
-  EXPECT_FLOAT_EQ(inv(25.0), hypergeometric_1f0(2, -4.0));
-  EXPECT_FLOAT_EQ(inv(65536), hypergeometric_1f0(16.0, 3));
-  EXPECT_FLOAT_EQ(531441.0, hypergeometric_1f0(-6.0, 10.0));
+  EXPECT_FLOAT_EQ(4.62962962963, hypergeometric_1f0(3, 0.4));
+  EXPECT_FLOAT_EQ(0.510204081633, hypergeometric_1f0(2, -0.4));
+  EXPECT_FLOAT_EQ(300.906354890, hypergeometric_1f0(16.0, 0.3));
+  EXPECT_FLOAT_EQ(0.531441, hypergeometric_1f0(-6.0, 0.1));
 }
 
 TEST(MathFunctions, hypergeometric_1f0_throw) {
   using stan::math::hypergeometric_1f0;
 
   EXPECT_THROW(hypergeometric_1f0(2.1, 1.0), std::domain_error);
   EXPECT_THROW(hypergeometric_1f0(0.5, 1.5), std::domain_error);
+  EXPECT_THROW(hypergeometric_1f0(0.5, -1.0), std::domain_error);
+  EXPECT_THROW(hypergeometric_1f0(0.5, -1.5), std::domain_error);
 }