commons-numbers-arrays/src/test/java/org/apache/commons/numbers/arrays/SafeNormTest.java

/*
 * 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.commons.numbers.arrays;

import org.junit.Assert;
import org.junit.Test;

/**
 * Test cases for the {@link SafeNorm} class.
 */
public class SafeNormTest {

    @Test
    public void testTiny() {
        final double s = 1e-320;
        final double[] v = new double[] { s, s };
        Assert.assertEquals(Math.sqrt(2) * s, SafeNorm.value(v), 0d);
    }

    @Test
    public void testBig() {
        final double s = 1e300;
        final double[] v = new double[] { s, s };
        Assert.assertEquals(Math.sqrt(2) * s, SafeNorm.value(v), 0d);
    }

    @Test
    public void testOne3D() {
        final double s = 1;
        final double[] v = new double[] { s, s, s };
        Assert.assertEquals(Math.sqrt(3), SafeNorm.value(v), 0d);
    }

    @Test
    public void testUnit3D() {
        Assert.assertEquals(1, SafeNorm.value(new double[] { 1, 0, 0 }), 0d);
        Assert.assertEquals(1, SafeNorm.value(new double[] { 0, 1, 0 }), 0d);
        Assert.assertEquals(1, SafeNorm.value(new double[] { 0, 0, 1 }), 0d);
    }

    @Test
    public void testSimple() {
        final double[] v = new double[] { -0.9, 8.7, -6.5, -4.3, -2.1, 0, 1.2, 3.4, -5.6, 7.8, 9.0 };
        double n = 0;
        for (int i = 0; i < v.length; i++) {
            n += v[i] * v[i];
        }
        final double expected = Math.sqrt(n);
        Assert.assertEquals(expected, SafeNorm.value(v), 0d);
    }
}