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 * https://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 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22
23 package org.hipparchus.ode.nonstiff;
24
25 import org.hipparchus.CalculusFieldElement;
26 import org.hipparchus.Field;
27 import org.hipparchus.ode.FieldEquationsMapper;
28 import org.hipparchus.ode.FieldODEStateAndDerivative;
29 import org.hipparchus.util.MathArrays;
30
31 /**
32 * This class implements a second order Runge-Kutta integrator for
33 * Ordinary Differential Equations.
34 *
35 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
36 * is the following one :</p>
37 * <pre>
38 * 0 | 0 0
39 * 1/2 | 1/2 0
40 * |----------
41 * | 0 1
42 * </pre>
43 *
44 * @see EulerFieldIntegrator
45 * @see ClassicalRungeKuttaFieldIntegrator
46 * @see GillFieldIntegrator
47 * @see ThreeEighthesFieldIntegrator
48 * @see LutherFieldIntegrator
49 *
50 * @param <T> the type of the field elements
51 */
52
53 public class MidpointFieldIntegrator<T extends CalculusFieldElement<T>> extends RungeKuttaFieldIntegrator<T> {
54
55 /** Name of integration scheme. */
56 public static final String METHOD_NAME = MidpointIntegrator.METHOD_NAME;
57
58 /** Simple constructor.
59 * Build a midpoint integrator with the given step.
60 * @param field field to which the time and state vector elements belong
61 * @param step integration step
62 */
63 public MidpointFieldIntegrator(final Field<T> field, final T step) {
64 super(field, METHOD_NAME, step);
65 }
66
67 /** {@inheritDoc} */
68 @Override
69 public T[] getC() {
70 final T[] c = MathArrays.buildArray(getField(), 1);
71 c[0] = getField().getOne().newInstance(0.5);
72 return c;
73 }
74
75 /** {@inheritDoc} */
76 @Override
77 public T[][] getA() {
78 final T[][] a = MathArrays.buildArray(getField(), 1, 1);
79 a[0][0] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 2);
80 return a;
81 }
82
83 /** {@inheritDoc} */
84 @Override
85 public T[] getB() {
86 final T[] b = MathArrays.buildArray(getField(), 2);
87 b[0] = getField().getZero();
88 b[1] = getField().getOne();
89 return b;
90 }
91
92 /** {@inheritDoc} */
93 @Override
94 protected MidpointFieldStateInterpolator<T>
95 createInterpolator(final boolean forward, T[][] yDotK,
96 final FieldODEStateAndDerivative<T> globalPreviousState,
97 final FieldODEStateAndDerivative<T> globalCurrentState,
98 final FieldEquationsMapper<T> mapper) {
99 return new MidpointFieldStateInterpolator<T>(getField(), forward, yDotK,
100 globalPreviousState, globalCurrentState,
101 globalPreviousState, globalCurrentState,
102 mapper);
103 }
104
105 }