commons-math-legacy/src/test/java/org/apache/commons/math4/legacy/analysis/interpolation/UnivariatePeriodicInterpolatorTest.java

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 * 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
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 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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 * See the License for the specific language governing permissions and
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package org.apache.commons.math4.legacy.analysis.interpolation;

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

import org.apache.commons.rng.UniformRandomProvider;
import org.apache.commons.rng.simple.RandomSource;

import org.apache.commons.math4.legacy.analysis.UnivariateFunction;
import org.apache.commons.math4.legacy.exception.NonMonotonicSequenceException;
import org.apache.commons.math4.legacy.exception.NumberIsTooSmallException;
import org.apache.commons.math4.core.jdkmath.JdkMath;


/**
 * Test for {@link UnivariatePeriodicInterpolator}.
 */
public class UnivariatePeriodicInterpolatorTest {
    private final UniformRandomProvider rng = RandomSource.KISS.create();

    @Test
    public void testSine() {
        final int n = 30;
        final double[] xval = new double[n];
        final double[] yval = new double[n];
        final double period = 12.3;
        final double offset = 45.67;

        double delta = 0;
        for (int i = 0; i < n; i++) {
            delta += rng.nextDouble() * period / n;
            xval[i] = offset + delta;
            yval[i] = JdkMath.sin(xval[i]);
        }

        final UnivariateInterpolator inter = new LinearInterpolator();
        final UnivariateFunction f = inter.interpolate(xval, yval);

        final UnivariateInterpolator interP
            = new UnivariatePeriodicInterpolator(new LinearInterpolator(),
                                                     period, 1);
        final UnivariateFunction fP = interP.interpolate(xval, yval);

        // Comparing with original interpolation algorithm.
        final double xMin = xval[0];
        final double xMax = xval[n - 1];
        for (int i = 0; i < n; i++) {
            final double x = xMin + (xMax - xMin) * rng.nextDouble();
            final double y = f.value(x);
            final double yP = fP.value(x);

            Assert.assertEquals("x=" + x, y, yP, Math.ulp(1d));
        }

        // Test interpolation outside the primary interval.
        for (int i = 0; i < n; i++) {
            final double xIn = offset + rng.nextDouble() * period;
            final double xOut = xIn + rng.nextInt(123456789) * period;
            final double yIn = fP.value(xIn);
            final double yOut = fP.value(xOut);

            Assert.assertEquals(yIn, yOut, 1e-7);
        }
    }

    @Test
    public void testLessThanOnePeriodCoverage() {
        final int n = 30;
        final double[] xval = new double[n];
        final double[] yval = new double[n];
        final double period = 12.3;
        final double offset = 45.67;

        double delta = period / 2;
        for (int i = 0; i < n; i++) {
            delta += period / (2 * n) * rng.nextDouble();
            xval[i] = offset + delta;
            yval[i] = JdkMath.sin(xval[i]);
        }

        final UnivariateInterpolator interP
            = new UnivariatePeriodicInterpolator(new LinearInterpolator(),
                                                     period, 1);
        final UnivariateFunction fP = interP.interpolate(xval, yval);

        // Test interpolation outside the sample data interval.
        for (int i = 0; i < n; i++) {
            final double xIn = offset + rng.nextDouble() * period;
            final double xOut = xIn + rng.nextInt(123456789) * period;
            final double yIn = fP.value(xIn);
            final double yOut = fP.value(xOut);

            Assert.assertEquals(yIn, yOut, 1e-7);
        }
    }

    @Test
    public void testMoreThanOnePeriodCoverage() {
        final int n = 30;
        final double[] xval = new double[n];
        final double[] yval = new double[n];
        final double period = 12.3;
        final double offset = 45.67;

        double delta = period / 2;
        for (int i = 0; i < n; i++) {
            delta += 10 * period / n * rng.nextDouble();
            xval[i] = offset + delta;
            yval[i] = JdkMath.sin(xval[i]);
        }

        final UnivariateInterpolator interP
            = new UnivariatePeriodicInterpolator(new LinearInterpolator(),
                                                     period, 1);
        final UnivariateFunction fP = interP.interpolate(xval, yval);

        // Test interpolation outside the sample data interval.
        for (int i = 0; i < n; i++) {
            final double xIn = offset + rng.nextDouble() * period;
            final double xOut = xIn + rng.nextInt(123456789) * period;
            final double yIn = fP.value(xIn);
            final double yOut = fP.value(xOut);

            Assert.assertEquals(yIn, yOut, 1e-6);
        }
    }

    @Test(expected=NumberIsTooSmallException.class)
    public void testTooFewSamples() {
        final double[] xval = { 2, 3, 7 };
        final double[] yval = { 1, 6, 5 };
        final double period = 10;

        final UnivariateInterpolator interpolator
            = new UnivariatePeriodicInterpolator(new LinearInterpolator(), period);
        interpolator.interpolate(xval, yval);
    }

    @Test(expected=NonMonotonicSequenceException.class)
    public void testUnsortedSamples() {
        final double[] xval = { 2, 3, 7, 4, 6 };
        final double[] yval = { 1, 6, 5, -1, -2 };
        final double period = 10;

        final UnivariateInterpolator interpolator
            = new UnivariatePeriodicInterpolator(new LinearInterpolator(), period);
        interpolator.interpolate(xval, yval);
    }
}