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.nonstiff; 19 20 import org.apache.commons.math.ode.DerivativeException; 21 import org.apache.commons.math.ode.sampling.StepInterpolator; 22 23 /** 24 * This class implements a linear interpolator for step. 25 * 26 * <p>This interpolator computes dense output inside the last 27 * step computed. The interpolation equation is consistent with the 28 * integration scheme : 29 * 30 * <pre> 31 * y(t_n + theta h) = y (t_n + h) - (1-theta) h y' 32 * </pre> 33 * 34 * where theta belongs to [0 ; 1] and where y' is the evaluation of 35 * the derivatives already computed during the step.</p> 36 * 37 * @see EulerIntegrator 38 * @version $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 fvr. 2011) $ 39 * @since 1.2 40 */ 41 42 class EulerStepInterpolator 43 extends RungeKuttaStepInterpolator { 44 45 /** Serializable version identifier */ 46 private static final long serialVersionUID = -7179861704951334960L; 47 48 /** Simple constructor. 49 * This constructor builds an instance that is not usable yet, the 50 * {@link 51 * org.apache.commons.math.ode.sampling.AbstractStepInterpolator#reinitialize} 52 * method should be called before using the instance in order to 53 * initialize the internal arrays. This constructor is used only 54 * in order to delay the initialization in some cases. The {@link 55 * RungeKuttaIntegrator} class uses the prototyping design pattern 56 * to create the step interpolators by cloning an uninitialized model 57 * and later initializing the copy. 58 */ 59 public EulerStepInterpolator() { 60 } 61 62 /** Copy constructor. 63 * @param interpolator interpolator to copy from. The copy is a deep 64 * copy: its arrays are separated from the original arrays of the 65 * instance 66 */ 67 public EulerStepInterpolator(final EulerStepInterpolator interpolator) { 68 super(interpolator); 69 } 70 71 /** {@inheritDoc} */ 72 @Override 73 protected StepInterpolator doCopy() { 74 return new EulerStepInterpolator(this); 75 } 76 77 78 /** {@inheritDoc} */ 79 @Override 80 protected void computeInterpolatedStateAndDerivatives(final double theta, 81 final double oneMinusThetaH) 82 throws DerivativeException { 83 84 for (int i = 0; i < interpolatedState.length; ++i) { 85 interpolatedState[i] = currentState[i] - oneMinusThetaH * yDotK[0][i]; 86 } 87 System.arraycopy(yDotK[0], 0, interpolatedDerivatives, 0, interpolatedDerivatives.length); 88 89 } 90 91 } 92