bug #1679: avoid possible division by 0 in complex-schur

1 files changed, 6 insertions, 3 deletions

diff --git a/Eigen/src/Eigenvalues/ComplexSchur.h b/Eigen/src/Eigenvalues/ComplexSchur.h
index b8b3490c6..fc71468f8 100644
--- a/Eigen/src/Eigenvalues/ComplexSchur.h
+++ b/Eigen/src/Eigenvalues/ComplexSchur.h
@@ -300,10 +300,13 @@ typename ComplexSchur<MatrixType>::ComplexScalar ComplexSchur<MatrixType>::compu
   ComplexScalar trace = t.coeff(0,0) + t.coeff(1,1);
   ComplexScalar eival1 = (trace + disc) / RealScalar(2);
   ComplexScalar eival2 = (trace - disc) / RealScalar(2);
-
-  if(numext::norm1(eival1) > numext::norm1(eival2))
+  RealScalar eival1_norm = numext::norm1(eival1);
+  RealScalar eival2_norm = numext::norm1(eival2);
+  // A division by zero can only occur if eival1==eival2==0.
+  // In this case, det==0, and all we have to do is checking that eival2_norm!=0
+  if(eival1_norm > eival2_norm)
     eival2 = det / eival1;
-  else
+  else if(eival2_norm!=RealScalar(0))
     eival1 = det / eival2;
 
   // choose the eigenvalue closest to the bottom entry of the diagonal