Raymond | dee0849 | 2015-04-02 10:43:13 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Licensed to the Apache Software Foundation (ASF) under one or more |
| 3 | * contributor license agreements. See the NOTICE file distributed with |
| 4 | * this work for additional information regarding copyright ownership. |
| 5 | * The ASF licenses this file to You under the Apache License, Version 2.0 |
| 6 | * (the "License"); you may not use this file except in compliance with |
| 7 | * the License. You may obtain a copy of the License at |
| 8 | * |
| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | * |
| 11 | * Unless required by applicable law or agreed to in writing, software |
| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | * See the License for the specific language governing permissions and |
| 15 | * limitations under the License. |
| 16 | */ |
| 17 | |
| 18 | package org.apache.commons.math.ode.sampling; |
| 19 | |
| 20 | import org.apache.commons.math.ode.DerivativeException; |
| 21 | import org.apache.commons.math.util.FastMath; |
| 22 | |
| 23 | /** |
| 24 | * This class wraps an object implementing {@link FixedStepHandler} |
| 25 | * into a {@link StepHandler}. |
| 26 | |
| 27 | * <p>This wrapper allows to use fixed step handlers with general |
| 28 | * integrators which cannot guaranty their integration steps will |
| 29 | * remain constant and therefore only accept general step |
| 30 | * handlers.</p> |
| 31 | * |
| 32 | * <p>The stepsize used is selected at construction time. The {@link |
| 33 | * FixedStepHandler#handleStep handleStep} method of the underlying |
| 34 | * {@link FixedStepHandler} object is called at the beginning time of |
| 35 | * the integration t0 and also at times t0+h, t0+2h, ... If the |
| 36 | * integration range is an integer multiple of the stepsize, then the |
| 37 | * last point handled will be the endpoint of the integration tend, if |
| 38 | * not, the last point will belong to the interval [tend - h ; |
| 39 | * tend].</p> |
| 40 | * |
| 41 | * <p>There is no constraint on the integrator, it can use any |
| 42 | * timestep it needs (time steps longer or shorter than the fixed time |
| 43 | * step and non-integer ratios are all allowed).</p> |
| 44 | * |
| 45 | * @see StepHandler |
| 46 | * @see FixedStepHandler |
| 47 | * @version $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 févr. 2011) $ |
| 48 | * @since 1.2 |
| 49 | */ |
| 50 | |
| 51 | public class StepNormalizer implements StepHandler { |
| 52 | |
| 53 | /** Fixed time step. */ |
| 54 | private double h; |
| 55 | |
| 56 | /** Underlying step handler. */ |
| 57 | private final FixedStepHandler handler; |
| 58 | |
| 59 | /** Last step time. */ |
| 60 | private double lastTime; |
| 61 | |
| 62 | /** Last State vector. */ |
| 63 | private double[] lastState; |
| 64 | |
| 65 | /** Last Derivatives vector. */ |
| 66 | private double[] lastDerivatives; |
| 67 | |
| 68 | /** Integration direction indicator. */ |
| 69 | private boolean forward; |
| 70 | |
| 71 | /** Simple constructor. |
| 72 | * @param h fixed time step (sign is not used) |
| 73 | * @param handler fixed time step handler to wrap |
| 74 | */ |
| 75 | public StepNormalizer(final double h, final FixedStepHandler handler) { |
| 76 | this.h = FastMath.abs(h); |
| 77 | this.handler = handler; |
| 78 | reset(); |
| 79 | } |
| 80 | |
| 81 | /** Determines whether this handler needs dense output. |
| 82 | * This handler needs dense output in order to provide data at |
| 83 | * regularly spaced steps regardless of the steps the integrator |
| 84 | * uses, so this method always returns true. |
| 85 | * @return always true |
| 86 | */ |
| 87 | public boolean requiresDenseOutput() { |
| 88 | return true; |
| 89 | } |
| 90 | |
| 91 | /** Reset the step handler. |
| 92 | * Initialize the internal data as required before the first step is |
| 93 | * handled. |
| 94 | */ |
| 95 | public void reset() { |
| 96 | lastTime = Double.NaN; |
| 97 | lastState = null; |
| 98 | lastDerivatives = null; |
| 99 | forward = true; |
| 100 | } |
| 101 | |
| 102 | /** |
| 103 | * Handle the last accepted step |
| 104 | * @param interpolator interpolator for the last accepted step. For |
| 105 | * efficiency purposes, the various integrators reuse the same |
| 106 | * object on each call, so if the instance wants to keep it across |
| 107 | * all calls (for example to provide at the end of the integration a |
| 108 | * continuous model valid throughout the integration range), it |
| 109 | * should build a local copy using the clone method and store this |
| 110 | * copy. |
| 111 | * @param isLast true if the step is the last one |
| 112 | * @throws DerivativeException this exception is propagated to the |
| 113 | * caller if the underlying user function triggers one |
| 114 | */ |
| 115 | public void handleStep(final StepInterpolator interpolator, final boolean isLast) |
| 116 | throws DerivativeException { |
| 117 | |
| 118 | if (lastState == null) { |
| 119 | |
| 120 | lastTime = interpolator.getPreviousTime(); |
| 121 | interpolator.setInterpolatedTime(lastTime); |
| 122 | lastState = interpolator.getInterpolatedState().clone(); |
| 123 | lastDerivatives = interpolator.getInterpolatedDerivatives().clone(); |
| 124 | |
| 125 | // take the integration direction into account |
| 126 | forward = interpolator.getCurrentTime() >= lastTime; |
| 127 | if (! forward) { |
| 128 | h = -h; |
| 129 | } |
| 130 | |
| 131 | } |
| 132 | |
| 133 | double nextTime = lastTime + h; |
| 134 | boolean nextInStep = forward ^ (nextTime > interpolator.getCurrentTime()); |
| 135 | while (nextInStep) { |
| 136 | |
| 137 | // output the stored previous step |
| 138 | handler.handleStep(lastTime, lastState, lastDerivatives, false); |
| 139 | |
| 140 | // store the next step |
| 141 | lastTime = nextTime; |
| 142 | interpolator.setInterpolatedTime(lastTime); |
| 143 | System.arraycopy(interpolator.getInterpolatedState(), 0, |
| 144 | lastState, 0, lastState.length); |
| 145 | System.arraycopy(interpolator.getInterpolatedDerivatives(), 0, |
| 146 | lastDerivatives, 0, lastDerivatives.length); |
| 147 | |
| 148 | nextTime += h; |
| 149 | nextInStep = forward ^ (nextTime > interpolator.getCurrentTime()); |
| 150 | |
| 151 | } |
| 152 | |
| 153 | if (isLast) { |
| 154 | // there will be no more steps, |
| 155 | // the stored one should be flagged as being the last |
| 156 | handler.handleStep(lastTime, lastState, lastDerivatives, true); |
| 157 | } |
| 158 | |
| 159 | } |
| 160 | |
| 161 | } |