[3936ad3] | 1 | /* j1.c |
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| 2 | * |
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| 3 | * Bessel function of order one |
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| 4 | * |
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| 5 | * |
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| 6 | * |
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| 7 | * SYNOPSIS: |
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| 8 | * |
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| 9 | * double x, y, j1(); |
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| 10 | * |
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| 11 | * y = j1( x ); |
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| 12 | * |
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| 13 | * |
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| 14 | * |
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| 15 | * DESCRIPTION: |
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| 16 | * |
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| 17 | * Returns Bessel function of order one of the argument. |
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| 18 | * |
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| 19 | * The domain is divided into the intervals [0, 8] and |
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| 20 | * (8, infinity). In the first interval a 24 term Chebyshev |
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| 21 | * expansion is used. In the second, the asymptotic |
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| 22 | * trigonometric representation is employed using two |
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| 23 | * rational functions of degree 5/5. |
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| 24 | * |
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| 25 | * |
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| 26 | * |
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| 27 | * ACCURACY: |
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| 28 | * |
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| 29 | * Absolute error: |
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| 30 | * arithmetic domain # trials peak rms |
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| 31 | * DEC 0, 30 10000 4.0e-17 1.1e-17 |
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| 32 | * IEEE 0, 30 30000 2.6e-16 1.1e-16 |
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| 33 | * |
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| 34 | * |
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| 35 | */ |
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| 36 | |
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| 37 | /* |
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| 38 | Cephes Math Library Release 2.8: June, 2000 |
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| 39 | Copyright 1984, 1987, 1989, 2000 by Stephen L. Moshier |
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| 40 | */ |
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[fad5dc1] | 41 | |
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[3f8584a2] | 42 | #if FLOAT_SIZE>4 |
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| 43 | //Cephes double pression function |
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[c8902ac] | 44 | double cephes_j1(double x); |
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[1596de3] | 45 | |
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[0b05c24] | 46 | constant double RPJ1[8] = { |
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| 47 | -8.99971225705559398224E8, |
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| 48 | 4.52228297998194034323E11, |
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| 49 | -7.27494245221818276015E13, |
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| 50 | 3.68295732863852883286E15, |
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| 51 | 0.0, |
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| 52 | 0.0, |
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| 53 | 0.0, |
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| 54 | 0.0 }; |
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| 55 | |
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| 56 | constant double RQJ1[8] = { |
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| 57 | 6.20836478118054335476E2, |
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| 58 | 2.56987256757748830383E5, |
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| 59 | 8.35146791431949253037E7, |
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| 60 | 2.21511595479792499675E10, |
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| 61 | 4.74914122079991414898E12, |
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| 62 | 7.84369607876235854894E14, |
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| 63 | 8.95222336184627338078E16, |
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| 64 | 5.32278620332680085395E18 |
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| 65 | }; |
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| 66 | |
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| 67 | constant double PPJ1[8] = { |
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| 68 | 7.62125616208173112003E-4, |
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| 69 | 7.31397056940917570436E-2, |
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| 70 | 1.12719608129684925192E0, |
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| 71 | 5.11207951146807644818E0, |
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| 72 | 8.42404590141772420927E0, |
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| 73 | 5.21451598682361504063E0, |
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| 74 | 1.00000000000000000254E0, |
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| 75 | 0.0} ; |
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| 76 | |
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| 77 | |
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| 78 | constant double PQJ1[8] = { |
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| 79 | 5.71323128072548699714E-4, |
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| 80 | 6.88455908754495404082E-2, |
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| 81 | 1.10514232634061696926E0, |
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| 82 | 5.07386386128601488557E0, |
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| 83 | 8.39985554327604159757E0, |
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| 84 | 5.20982848682361821619E0, |
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| 85 | 9.99999999999999997461E-1, |
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| 86 | 0.0 }; |
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| 87 | |
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| 88 | constant double QPJ1[8] = { |
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| 89 | 5.10862594750176621635E-2, |
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| 90 | 4.98213872951233449420E0, |
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| 91 | 7.58238284132545283818E1, |
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| 92 | 3.66779609360150777800E2, |
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| 93 | 7.10856304998926107277E2, |
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| 94 | 5.97489612400613639965E2, |
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| 95 | 2.11688757100572135698E2, |
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| 96 | 2.52070205858023719784E1 }; |
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| 97 | |
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| 98 | constant double QQJ1[8] = { |
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| 99 | 7.42373277035675149943E1, |
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| 100 | 1.05644886038262816351E3, |
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| 101 | 4.98641058337653607651E3, |
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| 102 | 9.56231892404756170795E3, |
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| 103 | 7.99704160447350683650E3, |
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| 104 | 2.82619278517639096600E3, |
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| 105 | 3.36093607810698293419E2, |
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| 106 | 0.0 }; |
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| 107 | |
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[c8902ac] | 108 | double cephes_j1(double x) |
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[3f8584a2] | 109 | { |
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| 110 | |
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[5181ccc] | 111 | double w, z, p, q, abs_x, sign_x; |
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[3f8584a2] | 112 | |
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| 113 | const double Z1 = 1.46819706421238932572E1; |
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| 114 | const double Z2 = 4.92184563216946036703E1; |
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| 115 | |
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[eb2946f] | 116 | // 2017-05-18 PAK - mathematica and mpmath use J1(-x) = -J1(x) |
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| 117 | if (x < 0) { |
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| 118 | abs_x = -x; |
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| 119 | sign_x = -1.0; |
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| 120 | } else { |
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| 121 | abs_x = x; |
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| 122 | sign_x = 1.0; |
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| 123 | } |
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[3f8584a2] | 124 | |
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[eb2946f] | 125 | if( abs_x <= 5.0 ) { |
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| 126 | z = abs_x * abs_x; |
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[3f8584a2] | 127 | w = polevl( z, RPJ1, 3 ) / p1evl( z, RQJ1, 8 ); |
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[eb2946f] | 128 | w = w * abs_x * (z - Z1) * (z - Z2); |
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| 129 | return( sign_x * w ); |
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[3f8584a2] | 130 | } |
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| 131 | |
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[eb2946f] | 132 | w = 5.0/abs_x; |
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[3f8584a2] | 133 | z = w * w; |
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| 134 | p = polevl( z, PPJ1, 6)/polevl( z, PQJ1, 6 ); |
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| 135 | q = polevl( z, QPJ1, 7)/p1evl( z, QQJ1, 7 ); |
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| 136 | |
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[5181ccc] | 137 | // 2017-05-19 PAK improve accuracy using trig identies |
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| 138 | // original: |
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| 139 | // const double THPIO4 = 2.35619449019234492885; |
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| 140 | // const double SQ2OPI = 0.79788456080286535588; |
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| 141 | // double sin_xn, cos_xn; |
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| 142 | // SINCOS(abs_x - THPIO4, sin_xn, cos_xn); |
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| 143 | // p = p * cos_xn - w * q * sin_xn; |
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| 144 | // return( sign_x * p * SQ2OPI / sqrt(abs_x) ); |
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| 145 | // expanding p*cos(a - 3 pi/4) - wq sin(a - 3 pi/4) |
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| 146 | // [ p(sin(a) - cos(a)) + wq(sin(a) + cos(a)) / sqrt(2) |
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| 147 | // note that sqrt(1/2) * sqrt(2/pi) = sqrt(1/pi) |
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| 148 | const double SQRT1_PI = 0.56418958354775628; |
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| 149 | double sin_x, cos_x; |
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| 150 | SINCOS(abs_x, sin_x, cos_x); |
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| 151 | p = p*(sin_x - cos_x) + w*q*(sin_x + cos_x); |
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| 152 | return( sign_x * p * SQRT1_PI / sqrt(abs_x) ); |
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[3f8584a2] | 153 | } |
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| 154 | |
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| 155 | #else |
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| 156 | //Single precission version of cephes |
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[c8902ac] | 157 | float cephes_j1f(float x); |
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[1596de3] | 158 | |
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[3f8584a2] | 159 | constant float JPJ1[8] = { |
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[0b05c24] | 160 | -4.878788132172128E-009, |
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| 161 | 6.009061827883699E-007, |
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| 162 | -4.541343896997497E-005, |
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| 163 | 1.937383947804541E-003, |
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| 164 | -3.405537384615824E-002, |
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| 165 | 0.0, |
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| 166 | 0.0, |
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| 167 | 0.0 |
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| 168 | }; |
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| 169 | |
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[3f8584a2] | 170 | constant float MO1J1[8] = { |
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[0b05c24] | 171 | 6.913942741265801E-002, |
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| 172 | -2.284801500053359E-001, |
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| 173 | 3.138238455499697E-001, |
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| 174 | -2.102302420403875E-001, |
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| 175 | 5.435364690523026E-003, |
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| 176 | 1.493389585089498E-001, |
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| 177 | 4.976029650847191E-006, |
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| 178 | 7.978845453073848E-001 |
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| 179 | }; |
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| 180 | |
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[3f8584a2] | 181 | constant float PH1J1[8] = { |
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[0b05c24] | 182 | -4.497014141919556E+001, |
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| 183 | 5.073465654089319E+001, |
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| 184 | -2.485774108720340E+001, |
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| 185 | 7.222973196770240E+000, |
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| 186 | -1.544842782180211E+000, |
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| 187 | 3.503787691653334E-001, |
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| 188 | -1.637986776941202E-001, |
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| 189 | 3.749989509080821E-001 |
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| 190 | }; |
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| 191 | |
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[eb2946f] | 192 | float cephes_j1f(float xx) |
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[0278e3f] | 193 | { |
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[3936ad3] | 194 | |
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[eb2946f] | 195 | float x, w, z, p, q, xn; |
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[0a9d219] | 196 | |
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[3f8584a2] | 197 | const float Z1 = 1.46819706421238932572E1; |
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[0a9d219] | 198 | |
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| 199 | |
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[eb2946f] | 200 | // 2017-05-18 PAK - mathematica and mpmath use J1(-x) = -J1(x) |
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| 201 | x = xx; |
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| 202 | if( x < 0 ) |
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| 203 | x = -xx; |
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[0a9d219] | 204 | |
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[eb2946f] | 205 | if( x <= 2.0 ) { |
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| 206 | z = x * x; |
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| 207 | p = (z-Z1) * x * polevl( z, JPJ1, 4 ); |
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| 208 | return( xx < 0. ? -p : p ); |
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[3f8584a2] | 209 | } |
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[0a9d219] | 210 | |
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| 211 | q = 1.0/x; |
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| 212 | w = sqrt(q); |
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| 213 | |
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[95ce773] | 214 | p = w * polevl( q, MO1J1, 7); |
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[0a9d219] | 215 | w = q*q; |
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[5181ccc] | 216 | // 2017-05-19 PAK improve accuracy using trig identies |
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| 217 | // original: |
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| 218 | // const float THPIO4F = 2.35619449019234492885; /* 3*pi/4 */ |
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| 219 | // xn = q * polevl( w, PH1J1, 7) - THPIO4F; |
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| 220 | // p = p * cos(xn + x); |
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| 221 | // return( xx < 0. ? -p : p ); |
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| 222 | // expanding cos(a + b - 3 pi/4) is |
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| 223 | // [sin(a)sin(b) + sin(a)cos(b) + cos(a)sin(b)-cos(a)cos(b)] / sqrt(2) |
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| 224 | xn = q * polevl( w, PH1J1, 7); |
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| 225 | float cos_xn, sin_xn; |
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| 226 | float cos_x, sin_x; |
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| 227 | SINCOS(xn, sin_xn, cos_xn); // about xn and 1 |
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| 228 | SINCOS(x, sin_x, cos_x); |
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| 229 | p *= M_SQRT1_2*(sin_xn*(sin_x+cos_x) + cos_xn*(sin_x-cos_x)); |
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[0a9d219] | 230 | |
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[eb2946f] | 231 | return( xx < 0. ? -p : p ); |
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[fad5dc1] | 232 | } |
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[3f8584a2] | 233 | #endif |
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| 234 | |
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| 235 | #if FLOAT_SIZE>4 |
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[c8902ac] | 236 | #define sas_J1 cephes_j1 |
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[3f8584a2] | 237 | #else |
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[c8902ac] | 238 | #define sas_J1 cephes_j1f |
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[3f8584a2] | 239 | #endif |
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[fad5dc1] | 240 | |
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[95ce773] | 241 | //Finally J1c function that equals 2*J1(x)/x |
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[473a9f1] | 242 | double sas_2J1x_x(double x); |
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| 243 | double sas_2J1x_x(double x) |
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[0278e3f] | 244 | { |
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[19b9005] | 245 | return (x != 0.0 ) ? 2.0*sas_J1(x)/x : 1.0; |
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[95ce773] | 246 | } |
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