/**
* 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;
public final class Algebra {
private Algebra() {
}
public static Vector mult(Matrix m, Vector v) {
if (m.numRows() != v.size()) {
throw new CardinalityException(m.numRows(), v.size());
}
// Use a Dense Vector for the moment,
Vector result = new DenseVector(m.numRows());
for (int i = 0; i < m.numRows(); i++) {
result.set(i, m.viewRow(i).dot(v));
}
return result;
}
/** Returns sqrt(a^2 + b^2) without under/overflow. */
public static double hypot(double a, double b) {
double r;
if (Math.abs(a) > Math.abs(b)) {
r = b / a;
r = Math.abs(a) * Math.sqrt(1 + r * r);
} else if (b != 0) {
r = a / b;
r = Math.abs(b) * Math.sqrt(1 + r * r);
} else {
r = 0.0;
}
return r;
}
/**
* Compute Maximum Absolute Row Sum Norm of input Matrix m
* http://mathworld.wolfram.com/MaximumAbsoluteRowSumNorm.html
*/
public static double getNorm(Matrix m) {
double max = 0.0;
for (int i = 0; i < m.numRows(); i++) {
int sum = 0;
Vector cv = m.viewRow(i);
for (int j = 0; j < cv.size(); j++) {
sum += (int) Math.abs(cv.getQuick(j));
}
if (sum > max) {
max = sum;
}
}
return max;
}
}