Proper handling of domain errors.

1 files changed, 6 insertions, 1 deletions

diff --git a/Eigen/src/Core/SpecialFunctions.h b/Eigen/src/Core/SpecialFunctions.h
index 954972cdd..2dc7b22fc 100644
--- a/Eigen/src/Core/SpecialFunctions.h
+++ b/Eigen/src/Core/SpecialFunctions.h
@@ -970,9 +970,14 @@ struct polygamma_impl {
     static Scalar run(Scalar n, Scalar x) {
         Scalar zero = 0.0, one = 1.0;
         Scalar nplus = n + one;
+        const Scalar nan = NumTraits<Scalar>::quiet_NaN();
         
+        // Check that n is an integer
+        if (numext::floor(n) != n) {
+            return nan;
+        }
         // Just return the digamma function for n = 1
-        if (n == zero) {
+        else if (n == zero) {
             return digamma_impl<Scalar>::run(x);
         }
         // Use the same implementation as scipy