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Java example source code file (ClassicalRungeKuttaFieldIntegrator.java)

This example Java source code file (ClassicalRungeKuttaFieldIntegrator.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

classicalrungekuttafieldintegrator, classicalrungekuttafieldstepinterpolator, fieldequationsmapper, fieldodestateandderivative, override, realfieldelement, runge-kutta

The ClassicalRungeKuttaFieldIntegrator.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.nonstiff;

import org.apache.commons.math3.Field;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.ode.FieldEquationsMapper;
import org.apache.commons.math3.ode.FieldODEStateAndDerivative;
import org.apache.commons.math3.util.MathArrays;

/**
 * This class implements the classical fourth order Runge-Kutta
 * integrator for Ordinary Differential Equations (it is the most
 * often used Runge-Kutta method).
 *
 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
 * is the following one :
 * <pre>
 *    0  |  0    0    0    0
 *   1/2 | 1/2   0    0    0
 *   1/2 |  0   1/2   0    0
 *    1  |  0    0    1    0
 *       |--------------------
 *       | 1/6  1/3  1/3  1/6
 * </pre>
 * </p>
 *
 * @see EulerFieldIntegrator
 * @see GillFieldIntegrator
 * @see MidpointFieldIntegrator
 * @see ThreeEighthesFieldIntegrator
 * @see LutherFieldIntegrator
 * @param <T> the type of the field elements
 * @since 3.6
 */

public class ClassicalRungeKuttaFieldIntegrator<T extends RealFieldElement
    extends RungeKuttaFieldIntegrator<T> {

    /** Simple constructor.
     * Build a fourth-order Runge-Kutta integrator with the given step.
     * @param field field to which the time and state vector elements belong
     * @param step integration step
     */
    public ClassicalRungeKuttaFieldIntegrator(final Field<T> field, final T step) {
        super(field, "classical Runge-Kutta", step);
    }

    /** {@inheritDoc} */
    public T[] getC() {
        final T[] c = MathArrays.buildArray(getField(), 3);
        c[0] = getField().getOne().multiply(0.5);
        c[1] = c[0];
        c[2] = getField().getOne();
        return c;
    }

    /** {@inheritDoc} */
    public T[][] getA() {
        final T[][] a = MathArrays.buildArray(getField(), 3, -1);
        for (int i = 0; i < a.length; ++i) {
            a[i] = MathArrays.buildArray(getField(), i + 1);
        }
        a[0][0] = fraction(1, 2);
        a[1][0] = getField().getZero();
        a[1][1] = a[0][0];
        a[2][0] = getField().getZero();
        a[2][1] = getField().getZero();
        a[2][2] = getField().getOne();
        return a;
    }

    /** {@inheritDoc} */
    public T[] getB() {
        final T[] b = MathArrays.buildArray(getField(), 4);
        b[0] = fraction(1, 6);
        b[1] = fraction(1, 3);
        b[2] = b[1];
        b[3] = b[0];
        return b;
    }

    /** {@inheritDoc} */
    @Override
    protected ClassicalRungeKuttaFieldStepInterpolator<T>
        createInterpolator(final boolean forward, T[][] yDotK,
                           final FieldODEStateAndDerivative<T> globalPreviousState,
                           final FieldODEStateAndDerivative<T> globalCurrentState,
                           final FieldEquationsMapper<T> mapper) {
        return new ClassicalRungeKuttaFieldStepInterpolator<T>(getField(), forward, yDotK,
                                                               globalPreviousState, globalCurrentState,
                                                               globalPreviousState, globalCurrentState,
                                                               mapper);
    }

}

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