From 945b0802c9521c9e2bf21ced7c0808fc6a48a151 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Fri, 20 Sep 2013 23:28:10 +0200
Subject: [PATCH] Reduce explicit zeros when applying SparseQR's matrix Q
 (grafted from 00dc45d0f912407366b20e132df76cffbbf22449 )

---
 Eigen/src/SparseQR/SparseQR.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Eigen/src/SparseQR/SparseQR.h b/Eigen/src/SparseQR/SparseQR.h
index 1bfa5ff13..afda43bfc 100644
--- a/Eigen/src/SparseQR/SparseQR.h
+++ b/Eigen/src/SparseQR/SparseQR.h
@@ -572,6 +572,7 @@ struct SparseQR_QProduct : ReturnByValue<SparseQR_QProduct<SparseQRType, Derived
         {
           Scalar tau = Scalar(0);
           tau = m_qr.m_Q.col(k).dot(res.col(j));
+          if(tau==Scalar(0)) continue;
           tau = tau * m_qr.m_hcoeffs(k);
           res.col(j) -= tau * m_qr.m_Q.col(k);
         }
@@ -587,6 +588,7 @@ struct SparseQR_QProduct : ReturnByValue<SparseQR_QProduct<SparseQRType, Derived
         {
           Scalar tau = Scalar(0);
           tau = m_qr.m_Q.col(k).dot(res.col(j));
+          if(tau==Scalar(0)) continue;
           tau = tau * m_qr.m_hcoeffs(k);
           res.col(j) -= tau * m_qr.m_Q.col(k);
         }