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Java example source code file (MicrosphereProjectionInterpolatorTest.java)

This example Java source code file (MicrosphereProjectionInterpolatorTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

illegalargumentexception, interpolatingmicrosphere2d, microsphereprojectioninterpolator, microsphereprojectioninterpolatortest, multivariatefunction, multivariateinterpolator, nan, number, test

The MicrosphereProjectionInterpolatorTest.java Java example source code

/*
 * 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.analysis.interpolation;

import org.apache.commons.math3.analysis.MultivariateFunction;
import org.apache.commons.math3.util.FastMath;
import org.junit.Assert;
import org.junit.Test;

/**
 * Test case for the {@link MicrosphereProjectionInterpolator
 * "microsphere projection"} interpolator.
 */
public final class MicrosphereProjectionInterpolatorTest {
    /**
     * Test of interpolator for a plane.
     * <p>
     * y = 2 x<sub>1 - 3 x2 + 5
     */
    @Test
    public void testLinearFunction2D() {
        MultivariateFunction f = new MultivariateFunction() {
            public double value(double[] x) {
                if (x.length != 2) {
                    throw new IllegalArgumentException();
                }
                return 2 * x[0] - 3 * x[1] + 5;
            }
        };

        final double darkFraction = 0.5;
        final double darkThreshold = 1e-2;
        final double background = Double.NaN;
        final double exponent = 1.1;
        final boolean shareSphere = true;
        final double noInterpolationTolerance = Math.ulp(1d);

        // N-dimensional interpolator.
        final MultivariateInterpolator interpolator
            = new MicrosphereProjectionInterpolator(2, 500,
                                                    darkFraction,
                                                    darkThreshold,
                                                    background,
                                                    exponent,
                                                    shareSphere,
                                                    noInterpolationTolerance);

        // 2D interpolator.
        final MultivariateInterpolator interpolator2D
            = new MicrosphereProjectionInterpolator(new InterpolatingMicrosphere2D(16,
                                                                                   darkFraction,
                                                                                   darkThreshold,
                                                                                   background),
                                                    exponent,
                                                    shareSphere,
                                                    noInterpolationTolerance);

        final double min = -1;
        final double max = 1;
        final double range = max - min;
        final int res = 5;
        final int n = res * res; // Number of sample points.
        final int dim = 2;
        double[][] x = new double[n][dim];
        double[] y = new double[n];
        int index = 0;
        for (int i = 0; i < res; i++) {
            final double x1Val = toCoordinate(min, range, res, i);
            for (int j = 0; j < res; j++) {
                final double x2Val = toCoordinate(min, range, res, j);
                x[index][0] = x1Val;
                x[index][1] = x2Val;
                y[index] = f.value(x[index]);
                ++index;
            }
        }

        final MultivariateFunction p = interpolator.interpolate(x, y);
        final MultivariateFunction p2D = interpolator2D.interpolate(x, y);

        double[] c = new double[dim];
        double expected, result, result2D;

        final int sampleIndex = 2;
        c[0] = x[sampleIndex][0];
        c[1] = x[sampleIndex][1];
        expected = f.value(c);
        result = p.value(c);
        result2D = p2D.value(c);
        Assert.assertEquals("on sample point (exact)", expected, result2D, FastMath.ulp(1d));
        Assert.assertEquals("on sample point (ND vs 2D)", result2D, result, FastMath.ulp(1d));

        // Interpolation.
        c[0] = 0.654321;
        c[1] = -0.345678;
        expected = f.value(c);
        result = p.value(c);
        result2D = p2D.value(c);
        Assert.assertEquals("interpolation (exact)", expected, result2D, 1e-1);
        Assert.assertEquals("interpolation (ND vs 2D)", result2D, result, 1e-1);

        // Extrapolation.
        c[0] = 0 - 1e-2;
        c[1] = 1 + 1e-2;
        expected = f.value(c);
        result = p.value(c);
        result2D = p2D.value(c);
        Assert.assertFalse(Double.isNaN(result));
        Assert.assertFalse(Double.isNaN(result2D));
        Assert.assertEquals("extrapolation (exact)", expected, result2D, 1e-1);
        Assert.assertEquals("extrapolation (ND vs 2D)", result2D, result, 1e-2);

        // Far away.
        c[0] = 20;
        c[1] = -30;
        result = p.value(c);
        Assert.assertTrue(result + " should be NaN", Double.isNaN(result));
        result2D = p2D.value(c);
        Assert.assertTrue(result2D + " should be NaN", Double.isNaN(result2D));
    }

    /**
     * @param min Minimum of the coordinate range.
     * @param range Extent of the coordinate interval.
     * @param res Number of pixels.
     * @param pixel Pixel index.
     */
    private static double toCoordinate(double min,
                                       double range,
                                       int res,
                                       int pixel) {
        return pixel * range / (res - 1) + min;
    }
}

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