From b0d08869a97b6ce94ce6590e91a1e7b79dd21f05 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Tue, 23 Jun 2015 14:54:31 +0200
Subject: [PATCH] Fix underflow in 3x3 tridiagonalization

---
 Eigen/src/Eigenvalues/Tridiagonalization.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Eigen/src/Eigenvalues/Tridiagonalization.h b/Eigen/src/Eigenvalues/Tridiagonalization.h
index a6fb00b21..f21331312 100644
--- a/Eigen/src/Eigenvalues/Tridiagonalization.h
+++ b/Eigen/src/Eigenvalues/Tridiagonalization.h
@@ -464,9 +464,10 @@ struct tridiagonalization_inplace_selector<MatrixType,3,false>
   static void run(MatrixType& mat, DiagonalType& diag, SubDiagonalType& subdiag, bool extractQ)
   {
     using std::sqrt;
+    const RealScalar tol = (std::numeric_limits<RealScalar>::min)();
     diag[0] = mat(0,0);
     RealScalar v1norm2 = numext::abs2(mat(2,0));
-    if(v1norm2 == RealScalar(0))
+    if(v1norm2 <= tol)
     {
       diag[1] = mat(1,1);
       diag[2] = mat(2,2);