/*
* 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;
/**
* This class implements a step interpolator for the 3/8 fourth
* order Runge-Kutta integrator.
*
* <p>This interpolator allows to compute dense output inside the last
* step computed. The interpolation equation is consistent with the
* integration scheme :
* <ul>
* <li>Using reference point at step start:<br>
* y(t<sub>n</sub> + θ h) = y (t<sub>n</sub>)
* + θ (h/8) [ (8 - 15 θ + 8 θ<sup>2</sup>) y'<sub>1</sub>
* + 3 * (15 θ - 12 θ<sup>2</sup>) y'<sub>2</sub>
* + 3 θ y'<sub>3</sub>
* + (-3 θ + 4 θ<sup>2</sup>) y'<sub>4</sub>
* ]
* </li>
* <li>Using reference point at step end:<br>
* y(t<sub>n</sub> + θ h) = y (t<sub>n</sub> + h)
* - (1 - θ) (h/8) [(1 - 7 θ + 8 θ<sup>2</sup>) y'<sub>1</sub>
* + 3 (1 + θ - 4 θ<sup>2</sup>) y'<sub>2</sub>
* + 3 (1 + θ) y'<sub>3</sub>
* + (1 + θ + 4 θ<sup>2</sup>) y'<sub>4</sub>
* ]
* </li>
* </ul>
* </p>
*
* where θ belongs to [0 ; 1] and where y'<sub>1</sub> to y'<sub>4</sub> are the four
* evaluations of the derivatives already computed during the
* step.</p>
*
* @see ThreeEighthesFieldIntegrator
* @param <T> the type of the field elements
* @since 3.6
*/
class ThreeEighthesFieldStepInterpolator<T extends RealFieldElement<T>>
extends RungeKuttaFieldStepInterpolator<T> {
/** Simple constructor.
* @param field field to which the time and state vector elements belong
* @param forward integration direction indicator
* @param yDotK slopes at the intermediate points
* @param globalPreviousState start of the global step
* @param globalCurrentState end of the global step
* @param softPreviousState start of the restricted step
* @param softCurrentState end of the restricted step
* @param mapper equations mapper for the all equations
*/
ThreeEighthesFieldStepInterpolator(final Field<T> field, final boolean forward,
final T[][] yDotK,
final FieldODEStateAndDerivative<T> globalPreviousState,
final FieldODEStateAndDerivative<T> globalCurrentState,
final FieldODEStateAndDerivative<T> softPreviousState,
final FieldODEStateAndDerivative<T> softCurrentState,
final FieldEquationsMapper<T> mapper) {
super(field, forward, yDotK,
globalPreviousState, globalCurrentState, softPreviousState, softCurrentState,
mapper);
}
/** {@inheritDoc} */
@Override
protected ThreeEighthesFieldStepInterpolator<T> create(final Field<T> newField, final boolean newForward, final T[][] newYDotK,
final FieldODEStateAndDerivative<T> newGlobalPreviousState,
final FieldODEStateAndDerivative<T> newGlobalCurrentState,
final FieldODEStateAndDerivative<T> newSoftPreviousState,
final FieldODEStateAndDerivative<T> newSoftCurrentState,
final FieldEquationsMapper<T> newMapper) {
return new ThreeEighthesFieldStepInterpolator<T>(newField, newForward, newYDotK,
newGlobalPreviousState, newGlobalCurrentState,
newSoftPreviousState, newSoftCurrentState,
newMapper);
}
/** {@inheritDoc} */
@SuppressWarnings("unchecked")
@Override
protected FieldODEStateAndDerivative<T> computeInterpolatedStateAndDerivatives(final FieldEquationsMapper<T> mapper,
final T time, final T theta,
final T thetaH, final T oneMinusThetaH) {
final T coeffDot3 = theta.multiply(0.75);
final T coeffDot1 = coeffDot3.multiply(theta.multiply(4).subtract(5)).add(1);
final T coeffDot2 = coeffDot3.multiply(theta.multiply(-6).add(5));
final T coeffDot4 = coeffDot3.multiply(theta.multiply(2).subtract(1));
final T[] interpolatedState;
final T[] interpolatedDerivatives;
if (getGlobalPreviousState() != null && theta.getReal() <= 0.5) {
final T s = thetaH.divide(8);
final T fourTheta2 = theta.multiply(theta).multiply(4);
final T coeff1 = s.multiply(fourTheta2.multiply(2).subtract(theta.multiply(15)).add(8));
final T coeff2 = s.multiply(theta.multiply(5).subtract(fourTheta2)).multiply(3);
final T coeff3 = s.multiply(theta).multiply(3);
final T coeff4 = s.multiply(fourTheta2.subtract(theta.multiply(3)));
interpolatedState = previousStateLinearCombination(coeff1, coeff2, coeff3, coeff4);
interpolatedDerivatives = derivativeLinearCombination(coeffDot1, coeffDot2, coeffDot3, coeffDot4);
} else {
final T s = oneMinusThetaH.divide(-8);
final T fourTheta2 = theta.multiply(theta).multiply(4);
final T thetaPlus1 = theta.add(1);
final T coeff1 = s.multiply(fourTheta2.multiply(2).subtract(theta.multiply(7)).add(1));
final T coeff2 = s.multiply(thetaPlus1.subtract(fourTheta2)).multiply(3);
final T coeff3 = s.multiply(thetaPlus1).multiply(3);
final T coeff4 = s.multiply(thetaPlus1.add(fourTheta2));
interpolatedState = currentStateLinearCombination(coeff1, coeff2, coeff3, coeff4);
interpolatedDerivatives = derivativeLinearCombination(coeffDot1, coeffDot2, coeffDot3, coeffDot4);
}
return new FieldODEStateAndDerivative<T>(time, interpolatedState, interpolatedDerivatives);
}
}