Commons Math example source code file (PolynomialSplineFunctionTest.java)

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

Java - Commons Math tags/keywords

exception, expecting, expecting, functionevaluationexception, illegalargumentexception, illegalargumentexception, polynomialfunction, polynomialfunction, polynomialsplinefunction, polynomialsplinefunction, polynomialsplinefunctiontest, testcase, univariaterealfunction, util

The Commons Math PolynomialSplineFunctionTest.java 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.math.analysis.polynomials;

import java.util.Arrays;
import junit.framework.TestCase;

import org.apache.commons.math.FunctionEvaluationException;
import org.apache.commons.math.analysis.UnivariateRealFunction;

/**
 * Tests the PolynomialSplineFunction implementation.
 *
 * @version $Revision: 811685 $
 */
public class PolynomialSplineFunctionTest extends TestCase {

    /** Error tolerance for tests */
    protected double tolerance = 1.0e-12;

    /**
     * Quadratic polynomials used in tests:
     *
     * x^2 + x            [-1, 0)
     * x^2 + x + 2        [0, 1)
     * x^2 + x + 4        [1, 2)
     *
     * Defined so that evaluation using PolynomialSplineFunction evaluation
     * algorithm agrees at knot point boundaries.
     */
    protected PolynomialFunction[] polynomials = {
        new PolynomialFunction(new double[] {0d, 1d, 1d}),
        new PolynomialFunction(new double[] {2d, 1d, 1d}),
        new PolynomialFunction(new double[] {4d, 1d, 1d})
    };

    /** Knot points  */
    protected double[] knots = {-1, 0, 1, 2};

    /** Derivative of test polynomials -- 2x + 1  */
    protected PolynomialFunction dp =
        new PolynomialFunction(new double[] {1d, 2d});


    public void testConstructor() {
        PolynomialSplineFunction spline =
            new PolynomialSplineFunction(knots, polynomials);
        assertTrue(Arrays.equals(knots, spline.getKnots()));
        assertEquals(1d, spline.getPolynomials()[0].getCoefficients()[2], 0);
        assertEquals(3, spline.getN());

        try { // too few knots
            new PolynomialSplineFunction(new double[] {0}, polynomials);
            fail("Expecting IllegalArgumentException");
        } catch (IllegalArgumentException ex) {
            // expected
        }

        try { // too many knots
            new PolynomialSplineFunction(new double[] {0,1,2,3,4}, polynomials);
            fail("Expecting IllegalArgumentException");
        } catch (IllegalArgumentException ex) {
            // expected
        }

        try { // knots not increasing
            new PolynomialSplineFunction(new double[] {0,1, 3, 2}, polynomials);
            fail("Expecting IllegalArgumentException");
        } catch (IllegalArgumentException ex) {
            // expected
        }
    }

    public void testValues() throws Exception {
        PolynomialSplineFunction spline =
            new PolynomialSplineFunction(knots, polynomials);
        UnivariateRealFunction dSpline = spline.derivative();

        /**
         * interior points -- spline value at x should equal p(x - knot)
         * where knot is the largest knot point less than or equal to x and p
         * is the polynomial defined over the knot segment to which x belongs.
         */
        double x = -1;
        int index = 0;
        for (int i = 0; i < 10; i++) {
           x+=0.25;
           index = findKnot(knots, x);
           assertEquals("spline function evaluation failed for x=" + x,
                   polynomials[index].value(x - knots[index]), spline.value(x), tolerance);
           assertEquals("spline derivative evaluation failed for x=" + x,
                   dp.value(x - knots[index]), dSpline.value(x), tolerance);
        }

        // knot points -- centering should zero arguments
        for (int i = 0; i < 3; i++) {
            assertEquals("spline function evaluation failed for knot=" + knots[i],
                    polynomials[i].value(0), spline.value(knots[i]), tolerance);
            assertEquals("spline function evaluation failed for knot=" + knots[i],
                    dp.value(0), dSpline.value(knots[i]), tolerance);
        }

        try { //outside of domain -- under min
            x = spline.value(-1.5);
            fail("Expecting IllegalArgumentException");
        } catch (FunctionEvaluationException ex) {
            // expected
        }

        try { //outside of domain -- over max
            x = spline.value(2.5);
            fail("Expecting IllegalArgumentException");
        } catch (FunctionEvaluationException ex) {
            // expected
        }
    }

    /**
     *  Do linear search to find largest knot point less than or equal to x.
     *  Implementation does binary search.
     */
     protected int findKnot(double[] knots, double x) {
         if (x < knots[0] || x >= knots[knots.length -1]) {
             throw new IllegalArgumentException("x is out of range");
         }
         for (int i = 0; i < knots.length; i++) {
             if (knots[i] > x) {
                 return i -1;
             }
         }
         throw new IllegalArgumentException("x is out of range");
     }
}