/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.mahout.math.solver;
import org.apache.mahout.math.DenseVector;
import org.apache.mahout.math.Matrix;
import org.apache.mahout.math.Vector;
/**
* Implements the Jacobi preconditioner for a matrix A. This is defined as inv(diag(A)).
*/
public final class JacobiConditioner implements Preconditioner {
private final DenseVector inverseDiagonal;
public JacobiConditioner(Matrix a) {
if (a.numCols() != a.numRows()) {
throw new IllegalArgumentException("Matrix must be square.");
}
inverseDiagonal = new DenseVector(a.numCols());
for (int i = 0; i < a.numCols(); ++i) {
inverseDiagonal.setQuick(i, 1.0 / a.getQuick(i, i));
}
}
@Override
public Vector precondition(Vector v) {
return v.times(inverseDiagonal);
}
}