MATH-1389: Performance improvement for Array2DRowRealMatrix.getSubMat…

…rix()
apache · Oct 12, 2016 · 72df12f · 72df12f
1 parent f672e82
commit 72df12f
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diff --git a/src/changes/changes.xml b/src/changes/changes.xml
@@ -54,6 +54,9 @@ If the output is not quite correct, check for invisible trailing spaces!
     </release>
 
     <release version="4.0" date="XXXX-XX-XX" description="">
+      <action dev="ebourg" type="update" issue="MATH-1389" due-to="Christoph Dibak">
+        Performance improvement for Array2DRowRealMatrix.getSubMatrix()
+      </action>
       <action dev="erans" type="add" issue="MATH-1383">
         Dependency toward the "Commons Rng" component.
       </action>

diff --git a/src/main/java/org/apache/commons/math4/linear/Array2DRowRealMatrix.java b/src/main/java/org/apache/commons/math4/linear/Array2DRowRealMatrix.java
@@ -388,6 +388,24 @@ public double[] preMultiply(final double[] v)
 
     }
 
+    /** {@inheritDoc} */
+    @Override
+    public RealMatrix getSubMatrix(final int startRow, final int endRow, 
+                                   final int startColumn, final int endColumn)
+            throws OutOfRangeException, NumberIsTooSmallException {
+        MatrixUtils.checkSubMatrixIndex(this, startRow, endRow, startColumn, endColumn);
+        final int rowCount = endRow - startRow + 1;
+        final int columnCount = endColumn - startColumn + 1;
+        final double[][] outData = new double[rowCount][columnCount];
+        for (int i = 0; i < rowCount; ++i) {
+            System.arraycopy(data[startRow + i], startColumn, outData[i], 0, columnCount);
+        }
+
+        Array2DRowRealMatrix subMatrix = new Array2DRowRealMatrix();
+        subMatrix.data = outData;
+        return subMatrix;
+    }
+
     /** {@inheritDoc} */
     @Override
     public double walkInRowOrder(final RealMatrixChangingVisitor visitor) {