From a08f9179d33966cc61cc42a91538bc04499ce265 Mon Sep 17 00:00:00 2001
From: Gilles Sadowski <erans@apache.org>
Date: Sun, 2 Oct 2011 13:00:41 +0000
Subject: [PATCH] MATH-676 Faster "multiply" method.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1178186 13f79535-47bb-0310-9956-ffa450edef68
---
 .../math/linear/Array2DRowRealMatrix.java     | 24 +++++++++++++------
 src/site/xdoc/changes.xml                     |  4 ++++
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/src/main/java/org/apache/commons/math/linear/Array2DRowRealMatrix.java b/src/main/java/org/apache/commons/math/linear/Array2DRowRealMatrix.java
index 981d2c72b..8d448dc50 100644
--- a/src/main/java/org/apache/commons/math/linear/Array2DRowRealMatrix.java
+++ b/src/main/java/org/apache/commons/math/linear/Array2DRowRealMatrix.java
@@ -212,21 +212,31 @@ public class Array2DRowRealMatrix extends AbstractRealMatrix implements Serializ
         final int nRows = this.getRowDimension();
         final int nCols = m.getColumnDimension();
         final int nSum = this.getColumnDimension();
+
         final double[][] outData = new double[nRows][nCols];
-        for (int row = 0; row < nRows; row++) {
-            final double[] dataRow    = data[row];
-            final double[] outDataRow = outData[row];
-            for (int col = 0; col < nCols; col++) {
+        // Will hold a column of "m".
+        final double[] mCol = new double[nSum];
+        final double[][] mData = m.data;
+
+        // Multiply.
+        for (int col = 0; col < nCols; col++) {
+            // Copy all elements of column "col" of "m" so that
+            // will be in contiguous memory.
+            for (int mRow = 0; mRow < nSum; mRow++) {
+                mCol[mRow] = mData[mRow][col];
+            }
+
+            for (int row = 0; row < nRows; row++) {
+                final double[] dataRow = data[row];
                 double sum = 0;
                 for (int i = 0; i < nSum; i++) {
-                    sum += dataRow[i] * m.data[i][col];
+                    sum += dataRow[i] * mCol[i];
                 }
-                outDataRow[col] = sum;
+                outData[row][col] = sum;
             }
         }
 
         return new Array2DRowRealMatrix(outData, false);
-
     }
 
     /** {@inheritDoc} */
diff --git a/src/site/xdoc/changes.xml b/src/site/xdoc/changes.xml
index 0ee562178..a1e8e04f6 100644
--- a/src/site/xdoc/changes.xml
+++ b/src/site/xdoc/changes.xml
@@ -52,6 +52,10 @@ The <action> type attribute can be add,update,fix,remove.
     If the output is not quite correct, check for invisible trailing spaces!
      -->
     <release version="3.0" date="TBD" description="TBD">
+      <action dev="erans" type="fix" issue="MATH-676">
+         Faster "multiply" method in "Array2DRowRealMatrix". Code inspired
+         from the Jama project.
+      </action>
       <action dev="luc" type="fix" issue="MATH-445" >
         Replaced package.html with package-info.java for package documentation.
       </action>