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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 represents an interpolator over the last step during an
26   * ODE integration for the 5(4) Higham and Hall integrator.
27   *
28   * @see HighamHall54Integrator
29   *
30   * @version $Revision: 782432 $ $Date: 2009-06-07 15:08:26 -0400 (Sun, 07 Jun 2009) $
31   * @since 1.2
32   */
33  
34  class HighamHall54StepInterpolator
35    extends RungeKuttaStepInterpolator {
36  
37    /** Simple constructor.
38     * This constructor builds an instance that is not usable yet, the
39     * {@link AbstractStepInterpolator#reinitialize} method should be called
40     * before using the instance in order to initialize the internal arrays. This
41     * constructor is used only in order to delay the initialization in
42     * some cases. The {@link EmbeddedRungeKuttaIntegrator} uses the
43     * prototyping design pattern to create the step interpolators by
44     * cloning an uninitialized model and latter initializing the copy.
45     */
46    public HighamHall54StepInterpolator() {
47      super();
48    }
49  
50    /** Copy constructor.
51     * @param interpolator interpolator to copy from. The copy is a deep
52     * copy: its arrays are separated from the original arrays of the
53     * instance
54     */
55    public HighamHall54StepInterpolator(final HighamHall54StepInterpolator interpolator) {
56      super(interpolator);
57    }
58  
59    /** {@inheritDoc} */
60    @Override
61    protected StepInterpolator doCopy() {
62      return new HighamHall54StepInterpolator(this);
63    }
64  
65  
66    /** {@inheritDoc} */
67    @Override
68    protected void computeInterpolatedStateAndDerivatives(final double theta,
69                                            final double oneMinusThetaH)
70      throws DerivativeException {
71  
72      final double theta2 = theta * theta;
73  
74      final double b0 = h * (-1.0/12.0 + theta * (1.0 + theta * (-15.0/4.0 + theta * (16.0/3.0 + theta * -5.0/2.0))));
75      final double b2 = h * (-27.0/32.0 + theta2 * (459.0/32.0 + theta * (-243.0/8.0 + theta * 135.0/8.0)));
76      final double b3 = h * (4.0/3.0 + theta2 * (-22.0 + theta * (152.0/3.0  + theta * -30.0)));
77      final double b4 = h * (-125.0/96.0 + theta2 * (375.0/32.0 + theta * (-625.0/24.0 + theta * 125.0/8.0)));
78      final double b5 = h * (-5.0/48.0 + theta2 * (-5.0/16.0 + theta * 5.0/12.0));
79      final double bDot0 = 1 + theta * (-15.0/2.0 + theta * (16.0 - 10.0 * theta));
80      final double bDot2 = theta * (459.0/16.0 + theta * (-729.0/8.0 + 135.0/2.0 * theta));
81      final double bDot3 = theta * (-44.0 + theta * (152.0 - 120.0 * theta));
82      final double bDot4 = theta * (375.0/16.0 + theta * (-625.0/8.0 + 125.0/2.0 * theta));
83      final double bDot5 = theta * 5.0/8.0 * (2 * theta - 1);
84  
85      for (int i = 0; i < interpolatedState.length; ++i) {
86          final double yDot0 = yDotK[0][i];
87          final double yDot2 = yDotK[2][i];
88          final double yDot3 = yDotK[3][i];
89          final double yDot4 = yDotK[4][i];
90          final double yDot5 = yDotK[5][i];
91          interpolatedState[i] =
92              currentState[i] + b0 * yDot0 + b2 * yDot2 + b3 * yDot3 + b4 * yDot4 + b5 * yDot5;
93          interpolatedDerivatives[i] =
94              bDot0 * yDot0 + bDot2 * yDot2 + bDot3 * yDot3 + bDot4 * yDot4 + bDot5 * yDot5;
95      }
96  
97    }
98  
99    /** Serializable version identifier */
100   private static final long serialVersionUID = -3583240427587318654L;
101 
102 }