Commons Math example source code file (StepNormalizer.java)

This example Commons Math source code file (StepNormalizer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Math tags/keywords

derivativeexception, fixedstephandler, fixedstephandler, stephandler, stephandler, stepinterpolator, stepinterpolator, stepnormalizer, stepnormalizer

The Commons Math StepNormalizer.java 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.math.ode.sampling;

import org.apache.commons.math.ode.DerivativeException;

/**
 * This class wraps an object implementing {@link FixedStepHandler}
 * into a {@link StepHandler}.

 * <p>This wrapper allows to use fixed step handlers with general
 * integrators which cannot guaranty their integration steps will
 * remain constant and therefore only accept general step
 * handlers.</p>
 *
 * <p>The stepsize used is selected at construction time. The {@link
 * FixedStepHandler#handleStep handleStep} method of the underlying
 * {@link FixedStepHandler} object is called at the beginning time of
 * the integration t0 and also at times t0+h, t0+2h, ... If the
 * integration range is an integer multiple of the stepsize, then the
 * last point handled will be the endpoint of the integration tend, if
 * not, the last point will belong to the interval [tend - h ;
 * tend].</p>
 *
 * <p>There is no constraint on the integrator, it can use any
 * timestep it needs (time steps longer or shorter than the fixed time
 * step and non-integer ratios are all allowed).</p>
 *
 * @see StepHandler
 * @see FixedStepHandler
 * @version $Revision: 811833 $ $Date: 2009-09-06 12:27:50 -0400 (Sun, 06 Sep 2009) $
 * @since 1.2
 */

public class StepNormalizer implements StepHandler {

    /** Fixed time step. */
    private double h;

    /** Underlying step handler. */
    private final FixedStepHandler handler;

    /** Last step time. */
    private double lastTime;

    /** Last State vector. */
    private double[] lastState;

    /** Last Derivatives vector. */
    private double[] lastDerivatives;

    /** Integration direction indicator. */
    private boolean forward;

    /** Simple constructor.
     * @param h fixed time step (sign is not used)
     * @param handler fixed time step handler to wrap
     */
    public StepNormalizer(final double h, final FixedStepHandler handler) {
        this.h       = Math.abs(h);
        this.handler = handler;
        reset();
    }

    /** Determines whether this handler needs dense output.
     * This handler needs dense output in order to provide data at
     * regularly spaced steps regardless of the steps the integrator
     * uses, so this method always returns true.
     * @return always true
     */
    public boolean requiresDenseOutput() {
        return true;
    }

    /** Reset the step handler.
     * Initialize the internal data as required before the first step is
     * handled.
     */
    public void reset() {
        lastTime        = Double.NaN;
        lastState       = null;
        lastDerivatives = null;
        forward         = true;
    }

    /**
     * Handle the last accepted step
     * @param interpolator interpolator for the last accepted step. For
     * efficiency purposes, the various integrators reuse the same
     * object on each call, so if the instance wants to keep it across
     * all calls (for example to provide at the end of the integration a
     * continuous model valid throughout the integration range), it
     * should build a local copy using the clone method and store this
     * copy.
     * @param isLast true if the step is the last one
     * @throws DerivativeException this exception is propagated to the
     * caller if the underlying user function triggers one
     */
    public void handleStep(final StepInterpolator interpolator, final boolean isLast)
        throws DerivativeException {

        if (lastState == null) {

            lastTime = interpolator.getPreviousTime();
            interpolator.setInterpolatedTime(lastTime);
            lastState = interpolator.getInterpolatedState().clone();
            lastDerivatives = interpolator.getInterpolatedDerivatives().clone();

            // take the integration direction into account
            forward = interpolator.getCurrentTime() >= lastTime;
            if (! forward) {
                h = -h;
            }

        }

        double nextTime = lastTime + h;
        boolean nextInStep = forward ^ (nextTime > interpolator.getCurrentTime());
        while (nextInStep) {

            // output the stored previous step
            handler.handleStep(lastTime, lastState, lastDerivatives, false);

            // store the next step
            lastTime = nextTime;
            interpolator.setInterpolatedTime(lastTime);
            System.arraycopy(interpolator.getInterpolatedState(), 0,
                             lastState, 0, lastState.length);
            System.arraycopy(interpolator.getInterpolatedDerivatives(), 0,
                             lastDerivatives, 0, lastDerivatives.length);

            nextTime  += h;
            nextInStep = forward ^ (nextTime > interpolator.getCurrentTime());

        }

        if (isLast) {
            // there will be no more steps,
            // the stored one should be flagged as being the last
            handler.handleStep(lastTime, lastState, lastDerivatives, true);
        }

    }

}