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18 package org.apache.commons.math.ode;
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37 public class TestProblem3
38 extends TestProblemAbstract {
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41 private static final long serialVersionUID = 8567328542728919999L;
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44 double e;
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47 private double[] y;
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53 public TestProblem3(double e) {
54 super();
55 this.e = e;
56 double[] y0 = { 1 - e, 0, 0, Math.sqrt((1+e)/(1-e)) };
57 setInitialConditions(0.0, y0);
58 setFinalConditions(20.0);
59 double[] errorScale = { 1.0, 1.0, 1.0, 1.0 };
60 setErrorScale(errorScale);
61 y = new double[y0.length];
62 }
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65
66
67 public TestProblem3() {
68 this(0.1);
69 }
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75 public TestProblem3(TestProblem3 problem) {
76 super(problem);
77 e = problem.e;
78 y = problem.y.clone();
79 }
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82 public TestProblem3 copy() {
83 return new TestProblem3(this);
84 }
85
86 @Override
87 public void doComputeDerivatives(double t, double[] y, double[] yDot) {
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90 double r2 = y[0] * y[0] + y[1] * y[1];
91 double invR3 = 1 / (r2 * Math.sqrt(r2));
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94 yDot[0] = y[2];
95 yDot[1] = y[3];
96 yDot[2] = -invR3 * y[0];
97 yDot[3] = -invR3 * y[1];
98
99 }
100
101 @Override
102 public double[] computeTheoreticalState(double t) {
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105 double E = t;
106 double d = 0;
107 double corr = 999.0;
108 for (int i = 0; (i < 50) && (Math.abs(corr) > 1.0e-12); ++i) {
109 double f2 = e * Math.sin(E);
110 double f0 = d - f2;
111 double f1 = 1 - e * Math.cos(E);
112 double f12 = f1 + f1;
113 corr = f0 * f12 / (f1 * f12 - f0 * f2);
114 d -= corr;
115 E = t + d;
116 };
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118 double cosE = Math.cos(E);
119 double sinE = Math.sin(E);
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121 y[0] = cosE - e;
122 y[1] = Math.sqrt(1 - e * e) * sinE;
123 y[2] = -sinE / (1 - e * cosE);
124 y[3] = Math.sqrt(1 - e * e) * cosE / (1 - e * cosE);
125
126 return y;
127 }
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129 }