commons-numbers-arrays/src/test/java/org/apache/commons/numbers/arrays/CosAngleTest.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.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

/**
 * Test cases for the {@link CosAngle} class.
 */
class CosAngleTest {

    @Test
    void testCosAngle2D() {
        double expected;

        final double[] v1 = {1, 0};
        expected = 1;
        Assertions.assertEquals(expected, CosAngle.value(v1, v1), 0d);

        final double[] v2 = {0, 1};
        expected = 0;
        Assertions.assertEquals(expected, CosAngle.value(v1, v2), 0d);

        final double[] v3 = {7, 7};
        expected = Math.sqrt(2) / 2;
        Assertions.assertEquals(expected, CosAngle.value(v1, v3), 1e-15);
        Assertions.assertEquals(expected, CosAngle.value(v3, v2), 1e-15);

        final double[] v4 = {-5, 0};
        expected = -1;
        Assertions.assertEquals(expected, CosAngle.value(v1, v4), 0);

        final double[] v5 = {-100, 100};
        expected = 0;
        Assertions.assertEquals(expected, CosAngle.value(v3, v5), 0);
    }

    @Test
    void testCosAngle3D() {
        double expected;

        final double[] v1 = {1, 1, 0};
        expected = 1;
        Assertions.assertEquals(expected, CosAngle.value(v1, v1), 1e-15);

        final double[] v2 = {1, 1, 1};
        expected = Math.sqrt(2) / Math.sqrt(3);
        Assertions.assertEquals(expected, CosAngle.value(v1, v2), 1e-15);
    }

    @Test
    void testCosAngleExtreme() {
        double expected;

        final double tiny = 1e-200;
        final double[] v1 = {tiny, tiny};
        final double big = 1e200;
        final double[] v2 = {-big, -big};
        expected = -1;
        Assertions.assertEquals(expected, CosAngle.value(v1, v2), 1e-15);

        final double[] v3 = {big, -big};
        expected = 0;
        Assertions.assertEquals(expected, CosAngle.value(v1, v3), 1e-15);
    }

    @Test
    void testCosAngle_dimensionMismatch() {
        final double[] a = {1.0};
        final double[] b = {1.0, 2.0};

        Assertions.assertThrows(IllegalArgumentException.class, () -> {
            CosAngle.value(a, b);
        });
    }
}