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Java example source code file (TestFieldProblem1.java)

This example Java source code file (TestFieldProblem1.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.

Learn more about this Java project at its project page.

Java - Java tags/keywords

fieldodestate, override, realfieldelement, testfieldproblem1, testfieldproblemabstract

The TestFieldProblem1.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.ode;

import org.apache.commons.math3.Field;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.util.MathArrays;

/**
 * This class is used in the junit tests for the ODE integrators.

 * <p>This specific problem is the following differential equation :
 * <pre>
 *    y' = -y
 * </pre>
 * the solution of this equation is a simple exponential function :
 * <pre>
 *   y (t) = y (t0) exp (t0-t)
 * </pre>
 * </p>

 * @param <T> the type of the field elements
 */
public class TestFieldProblem1<T extends RealFieldElement
    extends TestFieldProblemAbstract<T> {

    /**
     * Simple constructor.
     * @param field field to which elements belong
     */
    public TestFieldProblem1(Field<T> field) {
        super(field);
        setInitialConditions(convert(0.0), convert(1.0, 0.1));
        setFinalConditions(convert(4.0));
        setErrorScale(convert(1.0, 1.0));
    }

    @Override
    public T[] doComputeDerivatives(T t, T[] y) {

        final T[] yDot = MathArrays.buildArray(getField(), getDimension());

        // compute the derivatives
        for (int i = 0; i < getDimension(); ++i) {
            yDot[i] = y[i].negate();
        }

        return yDot;

    }

    @Override
    public T[] computeTheoreticalState(T t) {
        final FieldODEState<T> s0 = getInitialState();
        final T[] y0 = s0.getState();
        final T[] y = MathArrays.buildArray(getField(), getDimension());
        T c = s0.getTime().subtract(t).exp();
        for (int i = 0; i < getDimension(); ++i) {
            y[i] = c.multiply(y0[i]);
        }
        return y;
    }

}

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