From f5e1c896c7e95cecc776f20fc5663f67194a11cf Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Sat, 8 Aug 2009 00:01:43 +0200
Subject: [PATCH] replace custom rank one update in LU by an expression

---
 Eigen/src/LU/LU.h | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/Eigen/src/LU/LU.h b/Eigen/src/LU/LU.h
index 7d688c238..43154b769 100644
--- a/Eigen/src/LU/LU.h
+++ b/Eigen/src/LU/LU.h
@@ -434,16 +434,8 @@ void LU<MatrixType>::compute(const MatrixType& matrix)
     }
     if(k<rows-1)
       m_lu.col(k).end(rows-k-1) /= m_lu.coeff(k,k);
-    if(k<size-1) {
-      /* I know it's tempting to replace this for loop by a single matrix product. But actually there's no reason why it
-       * should be faster because it's just an exterior vector product; and in practice this gives much slower code with
-       * GCC 4.2-4.4 (this is weird, would be interesting to investigate). On the other hand, it would be worth having a variant
-       * for row-major matrices, traversing in the other direction for better performance, with a meta selector to compile only
-       * one path
-       */
-      for(int col = k + 1; col < cols; ++col)
-        m_lu.col(col).end(rows-k-1) -= m_lu.col(k).end(rows-k-1) * m_lu.coeff(k,col);
-    }
+    if(k<size-1)
+      m_lu.block(k+1,k+1,rows-k-1,cols-k-1) -= m_lu.col(k).end(rows-k-1) * m_lu.row(k).end(cols-k-1);
   }
 
   for(int k = 0; k < matrix.rows(); ++k) m_p.coeffRef(k) = k;