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/*
 * 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).
 *
 * 

This method is an explicit Runge-Kutta method, its Butcher-array * is the following one : *

 *    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
 * 
*

* * @see EulerFieldIntegrator * @see GillFieldIntegrator * @see MidpointFieldIntegrator * @see ThreeEighthesFieldIntegrator * @see LutherFieldIntegrator * @param the type of the field elements * @since 3.6 */ public class ClassicalRungeKuttaFieldIntegrator> extends RungeKuttaFieldIntegrator { /** 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 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 createInterpolator(final boolean forward, T[][] yDotK, final FieldODEStateAndDerivative globalPreviousState, final FieldODEStateAndDerivative globalCurrentState, final FieldEquationsMapper mapper) { return new ClassicalRungeKuttaFieldStepInterpolator(getField(), forward, yDotK, globalPreviousState, globalCurrentState, globalPreviousState, globalCurrentState, mapper); } }




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