From be10fc2a90cc9f7c2d8a928317f37988ce0a048e Mon Sep 17 00:00:00 2001
From: Chris Beall <chrisbeall@gmail.com>
Date: Fri, 11 Dec 2009 23:59:37 +0000
Subject: [PATCH] 18% performance boost by using pointer to address destination
 matrix A

---
 cpp/Matrix.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/cpp/Matrix.cpp b/cpp/Matrix.cpp
index 8650b39de..e5e0c5cfb 100644
--- a/cpp/Matrix.cpp
+++ b/cpp/Matrix.cpp
@@ -345,8 +345,12 @@ weighted_eliminate(Matrix& A, Vector& b, const Vector& sigmas) {
 		for (int i=0;i<m;++i) { // update all rows
 			double ai = a(i);
 			b(i) -= ai*d;
-			for (int j2=j+1;j2<n;++j2) // limit to only columns in separator
-				A(i,j2) -= ai*r(j2);
+			double *Aptr = A.data().begin()+i*n+j+1;
+			for (int j2=j+1;j2<n;++j2){ // limit to only columns in separator
+				//A(i,j2) -= ai*r(j2);
+				*Aptr -= ai*r(j2);
+				Aptr++;
+			}
 		}
 		if (verbose) print(sub(A,0,m,j+1,n), "updated A");
 		if (verbose) print(b, "updated b ");