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.AbstractStepInterpolator;
22 import org.apache.commons.math.ode.sampling.StepInterpolator;
23
24 /**
25 * This class implements a linear interpolator for step.
26 *
27 * <p>This interpolator computes dense output inside the last
28 * step computed. The interpolation equation is consistent with the
29 * integration scheme :
30 *
31 * <pre>
32 * y(t_n + theta h) = y (t_n + h) - (1-theta) h y'
33 * </pre>
34 *
35 * where theta belongs to [0 ; 1] and where y' is the evaluation of
36 * the derivatives already computed during the step.</p>
37 *
38 * @see EulerIntegrator
39 * @version $Revision: 782432 $ $Date: 2009-06-07 15:08:26 -0400 (Sun, 07 Jun 2009) $
40 * @since 1.2
41 */
42
43 class EulerStepInterpolator
44 extends RungeKuttaStepInterpolator {
45
46 /** Serializable version identifier */
47 private static final long serialVersionUID = -7179861704951334960L;
48
49 /** Simple constructor.
50 * This constructor builds an instance that is not usable yet, the
51 * {@link AbstractStepInterpolator#reinitialize} method should be called
52 * before using the instance in order to initialize the internal arrays. This
53 * constructor is used only in order to delay the initialization in
54 * some cases. The {@link RungeKuttaIntegrator} class uses the
55 * prototyping design pattern to create the step interpolators by
56 * cloning an uninitialized model and latter initializing the copy.
57 */
58 public EulerStepInterpolator() {
59 }
60
61 /** Copy constructor.
62 * @param interpolator interpolator to copy from. The copy is a deep
63 * copy: its arrays are separated from the original arrays of the
64 * instance
65 */
66 public EulerStepInterpolator(final EulerStepInterpolator interpolator) {
67 super(interpolator);
68 }
69
70 /** {@inheritDoc} */
71 @Override
72 protected StepInterpolator doCopy() {
73 return new EulerStepInterpolator(this);
74 }
75
76
77 /** {@inheritDoc} */
78 @Override
79 protected void computeInterpolatedStateAndDerivatives(final double theta,
80 final double oneMinusThetaH)
81 throws DerivativeException {
82
83 for (int i = 0; i < interpolatedState.length; ++i) {
84 interpolatedState[i] = currentState[i] - oneMinusThetaH * yDotK[0][i];
85 }
86 System.arraycopy(yDotK[0], 0, interpolatedDerivatives, 0, interpolatedDerivatives.length);
87
88 }
89
90 }