RungeKuttaStateInterpolator.java

/*
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 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The Hipparchus project licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
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 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
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 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.hipparchus.ode.nonstiff.interpolators;

import org.hipparchus.ode.EquationsMapper;
import org.hipparchus.ode.ODEStateAndDerivative;
import org.hipparchus.ode.nonstiff.EmbeddedRungeKuttaIntegrator;
import org.hipparchus.ode.nonstiff.FixedStepRungeKuttaIntegrator;
import org.hipparchus.ode.sampling.AbstractODEStateInterpolator;

/** This class represents an interpolator over the last step during an
 * ODE integration for Runge-Kutta and embedded Runge-Kutta integrators.
 *
 * @see FixedStepRungeKuttaIntegrator
 * @see EmbeddedRungeKuttaIntegrator
 *
 */

public abstract class RungeKuttaStateInterpolator extends AbstractODEStateInterpolator {

    /** Serializable UID. */
    private static final long serialVersionUID = 20160328L;

    /** Slopes at the intermediate points */
    protected double[][] yDotK;

    /** Simple constructor.
     * @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
     */
    protected RungeKuttaStateInterpolator(final boolean forward,
                                          final double[][] yDotK,
                                          final ODEStateAndDerivative globalPreviousState,
                                          final ODEStateAndDerivative globalCurrentState,
                                          final ODEStateAndDerivative softPreviousState,
                                          final ODEStateAndDerivative softCurrentState,
                                          final EquationsMapper mapper) {
        super(forward, globalPreviousState, globalCurrentState, softPreviousState, softCurrentState, mapper);
        this.yDotK = new double[yDotK.length][];
        for (int i = 0; i < yDotK.length; ++i) {
            this.yDotK[i] = yDotK[i].clone();
        }
    }

    /** {@inheritDoc} */
    @Override
    protected RungeKuttaStateInterpolator create(boolean newForward,
                                                 ODEStateAndDerivative newGlobalPreviousState,
                                                 ODEStateAndDerivative newGlobalCurrentState,
                                                 ODEStateAndDerivative newSoftPreviousState,
                                                 ODEStateAndDerivative newSoftCurrentState,
                                                 EquationsMapper newMapper) {
        return create(newForward, yDotK, newGlobalPreviousState, newGlobalCurrentState,
                      newSoftPreviousState, newSoftCurrentState, newMapper);
    }

    /** Create a new instance.
     * @param newForward integration direction indicator
     * @param newYDotK slopes at the intermediate points
     * @param newGlobalPreviousState start of the global step
     * @param newGlobalCurrentState end of the global step
     * @param newSoftPreviousState start of the restricted step
     * @param newSoftCurrentState end of the restricted step
     * @param newMapper equations mapper for the all equations
     * @return a new instance
     */
    protected abstract RungeKuttaStateInterpolator create(boolean newForward, double[][] newYDotK,
                                                          ODEStateAndDerivative newGlobalPreviousState,
                                                          ODEStateAndDerivative newGlobalCurrentState,
                                                          ODEStateAndDerivative newSoftPreviousState,
                                                          ODEStateAndDerivative newSoftCurrentState,
                                                          EquationsMapper newMapper);

    /** Compute a state by linear combination added to previous state.
     * @param coefficients coefficients to apply to the method staged derivatives
     * @return combined state
     */
    protected final double[] previousStateLinearCombination(final double ... coefficients) {
        return combine(getGlobalPreviousState().getCompleteState(),
                       coefficients);
    }

    /** Compute a state by linear combination added to current state.
     * @param coefficients coefficients to apply to the method staged derivatives
     * @return combined state
     */
    protected double[] currentStateLinearCombination(final double ... coefficients) {
        return combine(getGlobalCurrentState().getCompleteState(),
                       coefficients);
    }

    /** Compute a state derivative by linear combination.
     * @param coefficients coefficients to apply to the method staged derivatives
     * @return combined state
     */
    protected double[] derivativeLinearCombination(final double ... coefficients) {
        return combine(new double[yDotK[0].length], coefficients);
    }

    /** Linearly combine arrays.
     * @param a array to add to
     * @param coefficients coefficients to apply to the method staged derivatives
     * @return a itself, as a conveniency for fluent API
     */
    private double[] combine(final double[] a, final double ... coefficients) {
        for (int i = 0; i < a.length; ++i) {
            for (int k = 0; k < coefficients.length; ++k) {
                a[i] += coefficients[k] * yDotK[k][i];
            }
        }
        return a;
    }

}