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17 package org.apache.commons.numbers.gamma;
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24 final class InvGamma1pm1 {
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29 private static final double INV_GAMMA1P_M1_A0 = .611609510448141581788E-08;
30
31 private static final double INV_GAMMA1P_M1_A1 = .624730830116465516210E-08;
32
33 private static final double INV_GAMMA1P_M1_B1 = .203610414066806987300E+00;
34
35 private static final double INV_GAMMA1P_M1_B2 = .266205348428949217746E-01;
36
37 private static final double INV_GAMMA1P_M1_B3 = .493944979382446875238E-03;
38
39 private static final double INV_GAMMA1P_M1_B4 = -.851419432440314906588E-05;
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41 private static final double INV_GAMMA1P_M1_B5 = -.643045481779353022248E-05;
42
43 private static final double INV_GAMMA1P_M1_B6 = .992641840672773722196E-06;
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45 private static final double INV_GAMMA1P_M1_B7 = -.607761895722825260739E-07;
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47 private static final double INV_GAMMA1P_M1_B8 = .195755836614639731882E-09;
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49 private static final double INV_GAMMA1P_M1_P0 = .6116095104481415817861E-08;
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51 private static final double INV_GAMMA1P_M1_P1 = .6871674113067198736152E-08;
52
53 private static final double INV_GAMMA1P_M1_P2 = .6820161668496170657918E-09;
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55 private static final double INV_GAMMA1P_M1_P3 = .4686843322948848031080E-10;
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57 private static final double INV_GAMMA1P_M1_P4 = .1572833027710446286995E-11;
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59 private static final double INV_GAMMA1P_M1_P5 = -.1249441572276366213222E-12;
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61 private static final double INV_GAMMA1P_M1_P6 = .4343529937408594255178E-14;
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63 private static final double INV_GAMMA1P_M1_Q1 = .3056961078365221025009E+00;
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65 private static final double INV_GAMMA1P_M1_Q2 = .5464213086042296536016E-01;
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67 private static final double INV_GAMMA1P_M1_Q3 = .4956830093825887312020E-02;
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69 private static final double INV_GAMMA1P_M1_Q4 = .2692369466186361192876E-03;
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71 private static final double INV_GAMMA1P_M1_C = -.422784335098467139393487909917598E+00;
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73 private static final double INV_GAMMA1P_M1_C0 = .577215664901532860606512090082402E+00;
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75 private static final double INV_GAMMA1P_M1_C1 = -.655878071520253881077019515145390E+00;
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77 private static final double INV_GAMMA1P_M1_C2 = -.420026350340952355290039348754298E-01;
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79 private static final double INV_GAMMA1P_M1_C3 = .166538611382291489501700795102105E+00;
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81 private static final double INV_GAMMA1P_M1_C4 = -.421977345555443367482083012891874E-01;
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83 private static final double INV_GAMMA1P_M1_C5 = -.962197152787697356211492167234820E-02;
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85 private static final double INV_GAMMA1P_M1_C6 = .721894324666309954239501034044657E-02;
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87 private static final double INV_GAMMA1P_M1_C7 = -.116516759185906511211397108401839E-02;
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89 private static final double INV_GAMMA1P_M1_C8 = -.215241674114950972815729963053648E-03;
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91 private static final double INV_GAMMA1P_M1_C9 = .128050282388116186153198626328164E-03;
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93 private static final double INV_GAMMA1P_M1_C10 = -.201348547807882386556893914210218E-04;
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95 private static final double INV_GAMMA1P_M1_C11 = -.125049348214267065734535947383309E-05;
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97 private static final double INV_GAMMA1P_M1_C12 = .113302723198169588237412962033074E-05;
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99 private static final double INV_GAMMA1P_M1_C13 = -.205633841697760710345015413002057E-06;
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101
102 private InvGamma1pm1() {
103
104 }
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116 public static double value(final double x) {
117 if (x < -0.5 || x > 1.5) {
118 throw new GammaException(GammaException.OUT_OF_RANGE, x, -0.5, 1.5);
119 }
120
121 final double t = x <= 0.5 ? x : (x - 0.5) - 0.5;
122 if (t < 0) {
123 final double a = INV_GAMMA1P_M1_A0 + t * INV_GAMMA1P_M1_A1;
124 double b = INV_GAMMA1P_M1_B8;
125 b = INV_GAMMA1P_M1_B7 + t * b;
126 b = INV_GAMMA1P_M1_B6 + t * b;
127 b = INV_GAMMA1P_M1_B5 + t * b;
128 b = INV_GAMMA1P_M1_B4 + t * b;
129 b = INV_GAMMA1P_M1_B3 + t * b;
130 b = INV_GAMMA1P_M1_B2 + t * b;
131 b = INV_GAMMA1P_M1_B1 + t * b;
132 b = 1.0 + t * b;
133
134 double c = INV_GAMMA1P_M1_C13 + t * (a / b);
135 c = INV_GAMMA1P_M1_C12 + t * c;
136 c = INV_GAMMA1P_M1_C11 + t * c;
137 c = INV_GAMMA1P_M1_C10 + t * c;
138 c = INV_GAMMA1P_M1_C9 + t * c;
139 c = INV_GAMMA1P_M1_C8 + t * c;
140 c = INV_GAMMA1P_M1_C7 + t * c;
141 c = INV_GAMMA1P_M1_C6 + t * c;
142 c = INV_GAMMA1P_M1_C5 + t * c;
143 c = INV_GAMMA1P_M1_C4 + t * c;
144 c = INV_GAMMA1P_M1_C3 + t * c;
145 c = INV_GAMMA1P_M1_C2 + t * c;
146 c = INV_GAMMA1P_M1_C1 + t * c;
147 c = INV_GAMMA1P_M1_C + t * c;
148 if (x > 0.5) {
149 return t * c / x;
150 }
151 return x * ((c + 0.5) + 0.5);
152 }
153 double p = INV_GAMMA1P_M1_P6;
154 p = INV_GAMMA1P_M1_P5 + t * p;
155 p = INV_GAMMA1P_M1_P4 + t * p;
156 p = INV_GAMMA1P_M1_P3 + t * p;
157 p = INV_GAMMA1P_M1_P2 + t * p;
158 p = INV_GAMMA1P_M1_P1 + t * p;
159 p = INV_GAMMA1P_M1_P0 + t * p;
160
161 double q = INV_GAMMA1P_M1_Q4;
162 q = INV_GAMMA1P_M1_Q3 + t * q;
163 q = INV_GAMMA1P_M1_Q2 + t * q;
164 q = INV_GAMMA1P_M1_Q1 + t * q;
165 q = 1.0 + t * q;
166
167 double c = INV_GAMMA1P_M1_C13 + (p / q) * t;
168 c = INV_GAMMA1P_M1_C12 + t * c;
169 c = INV_GAMMA1P_M1_C11 + t * c;
170 c = INV_GAMMA1P_M1_C10 + t * c;
171 c = INV_GAMMA1P_M1_C9 + t * c;
172 c = INV_GAMMA1P_M1_C8 + t * c;
173 c = INV_GAMMA1P_M1_C7 + t * c;
174 c = INV_GAMMA1P_M1_C6 + t * c;
175 c = INV_GAMMA1P_M1_C5 + t * c;
176 c = INV_GAMMA1P_M1_C4 + t * c;
177 c = INV_GAMMA1P_M1_C3 + t * c;
178 c = INV_GAMMA1P_M1_C2 + t * c;
179 c = INV_GAMMA1P_M1_C1 + t * c;
180 c = INV_GAMMA1P_M1_C0 + t * c;
181
182 if (x > 0.5) {
183 return (t / x) * ((c - 0.5) - 0.5);
184 }
185 return x * c;
186 }
187 }