/*
* Copyright 2011-2015, by Vladimir Kostyukov and Contributors.
*
* This file is part of la4j project (http://la4j.org)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* You may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Contributor(s): -
*
*/
package org.la4j.inversion;
import org.la4j.Matrix;
public class NoPivotGaussInverter implements MatrixInverter {
private final Matrix matrix;
public NoPivotGaussInverter(final Matrix matrix) {
this.matrix = matrix;
}
@Override
public Matrix inverse() {
if (matrix.rows() != matrix.columns()) {
throw new IllegalArgumentException("Wrong matrix size: " + "rows != columns");
}
double var;
final Matrix result = matrix.copy();
for (int k = 0; k < matrix.rows(); k++) {
final double diagonalTerm = result.get(k, k);
if (Math.abs(diagonalTerm) <= Double.MIN_VALUE) {
throw new IllegalArgumentException(
"This matrix cannot be inverted with a non-pivoting Gauss elimination method.");
}
var = 1.0 / result.get(k, k);
result.set(k, k, 1.0);
for (int j = 0; j < matrix.rows(); j++) {
result.set(k, j, result.get(k, j) * var);
}
for (int i = 0; i < matrix.rows(); i++) {
if (i == k) {
continue;
}
var = result.get(i, k);
result.set(i, k, 0.0);
for (int j = 0; j < matrix.rows(); j++) {
result.set(i, j, result.get(i, j) - var * result.get(k, j));
}
}
}
return result;
}
@Override
public Matrix self() {
return matrix;
}
}