src/test/java/org/apache/commons/math3/transform/FastHadamardTransformerTest.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.math3.transform;

import org.apache.commons.math3.util.Precision;
import org.junit.Assert;
import org.junit.Test;


/**
 * JUnit Test for HadamardTransformerTest
 * @see org.apache.commons.math3.transform.FastHadamardTransformer
 */
public final class FastHadamardTransformerTest {

    /**
     * Test of transformer for the a 8-point FHT (means n=8)
     */
    @Test
    public void test8Points() {
        checkAllTransforms(new int[] { 1, 4, -2, 3, 0, 1, 4, -1 },
                       new int[] { 10, -4, 2, -4, 2, -12, 6, 8 });
    }

    /**
     * Test of transformer for the a 4-points FHT (means n=4)
     */
    @Test
    public void test4Points() {
        checkAllTransforms(new int[] { 1, 2, 3, 4 },
                           new int[] { 10, -2, -4, 0 });
    }

    /**
     * Test the inverse transform of an integer vector is not always an integer vector
     */
    @Test
    public void testNoIntInverse() {
        FastHadamardTransformer transformer = new FastHadamardTransformer();
        double[] x = transformer.transform(new double[] { 0, 1, 0, 1}, TransformType.INVERSE);
        Assert.assertEquals( 0.5, x[0], 0);
        Assert.assertEquals(-0.5, x[1], 0);
        Assert.assertEquals( 0.0, x[2], 0);
        Assert.assertEquals( 0.0, x[3], 0);
    }

    /**
     * Test of transformer for wrong number of points
     */
    @Test
    public void test3Points() {
        try {
            new FastHadamardTransformer().transform(new double[3], TransformType.FORWARD);
            Assert.fail("an exception should have been thrown");
        } catch (IllegalArgumentException iae) {
            // expected
        }
    }

    private void checkAllTransforms(int[]x, int[] y) {
        checkDoubleTransform(x, y);
        checkInverseDoubleTransform(x, y);
        checkIntTransform(x, y);
    }

    private void checkDoubleTransform(int[]x, int[] y) {
        // Initiate the transformer
        FastHadamardTransformer transformer = new FastHadamardTransformer();

        // check double transform
        double[] dX = new double[x.length];
        for (int i = 0; i < dX.length; ++i) {
            dX[i] = x[i];
        }
        double dResult[] = transformer.transform(dX, TransformType.FORWARD);
        for (int i = 0; i < dResult.length; i++) {
            // compare computed results to precomputed results
            Assert.assertTrue(Precision.equals(y[i], dResult[i], 1));
        }
    }

    private void checkIntTransform(int[]x, int[] y) {
        // Initiate the transformer
        FastHadamardTransformer transformer = new FastHadamardTransformer();

        // check integer transform
        int iResult[] = transformer.transform(x);
        for (int i = 0; i < iResult.length; i++) {
            // compare computed results to precomputed results
            Assert.assertEquals(y[i], iResult[i]);
        }

    }

    private void checkInverseDoubleTransform(int[]x, int[] y) {
        // Initiate the transformer
        FastHadamardTransformer transformer = new FastHadamardTransformer();

        // check double transform
        double[] dY = new double[y.length];
        for (int i = 0; i < dY.length; ++i) {
            dY[i] = y[i];
        }
        double dResult[] = transformer.transform(dY, TransformType.INVERSE);
        for (int i = 0; i < dResult.length; i++) {
            // compare computed results to precomputed results
            Assert.assertTrue(Precision.equals(x[i], dResult[i], 1));
        }

    }

}