Fixed bug #702 and added unit test.

Thanks to Alexander Werner for the report.

1 files changed, 3 insertions, 5 deletions

diff --git a/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h b/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
index 8d42e69b9..590797973 100644
--- a/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
+++ b/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
@@ -599,12 +599,10 @@ atan2(const AutoDiffScalar<DerTypeA>& a, const AutoDiffScalar<DerTypeB>& b)
   PlainADS ret;
   ret.value() = atan2(a.value(), b.value());
   
-  Scalar tmp2 = a.value() * a.value();
-  Scalar tmp3 = b.value() * b.value();
-  Scalar tmp4 = tmp3/(tmp2+tmp3);
+  Scalar squared_hypot = a.value() * a.value() + b.value() * b.value();
   
-  if (tmp4!=0)
-    ret.derivatives() = (a.derivatives() * b.value() - a.value() * b.derivatives()) * (tmp2+tmp3);
+  // if (squared_hypot==0) the derivation is undefined and the following results in a NaN:
+  ret.derivatives() = (a.derivatives() * b.value() - a.value() * b.derivatives()) / squared_hypot;
 
   return ret;
 }