3 * Modified Bessel function of order one
17 * Returns modified Bessel function of order one of the
20 * The function is defined as i1(x) = -i j1( ix ).
22 * The range is partitioned into the two intervals [0,8] and
23 * (8, infinity). Chebyshev polynomial expansions are employed
31 * arithmetic domain # trials peak rms
32 * IEEE 0, 30 100000 1.5e-6 1.6e-7
38 * Modified Bessel function of order one,
39 * exponentially scaled
53 * Returns exponentially scaled modified Bessel function
54 * of order one of the argument.
56 * The function is defined as i1(x) = -i exp(-|x|) j1( ix ).
63 * arithmetic domain # trials peak rms
64 * IEEE 0, 30 30000 1.5e-6 1.5e-7
73 Cephes Math Library Release 2.0: March, 1987
74 Copyright 1985, 1987 by Stephen L. Moshier
75 Direct inquiries to 30 Frost Street, Cambridge, MA 02140
80 /* Chebyshev coefficients for exp(-x) I1(x) / x
81 * in the interval [0,8].
83 * lim(x->0){ exp(-x) I1(x) / x } = 1/2.
88 9.38153738649577178388E-9f,
89 -4.44505912879632808065E-8f,
90 2.00329475355213526229E-7f,
91 -8.56872026469545474066E-7f,
92 3.47025130813767847674E-6f,
93 -1.32731636560394358279E-5f,
94 4.78156510755005422638E-5f,
95 -1.61760815825896745588E-4f,
96 5.12285956168575772895E-4f,
97 -1.51357245063125314899E-3f,
98 4.15642294431288815669E-3f,
99 -1.05640848946261981558E-2f,
100 2.47264490306265168283E-2f,
101 -5.29459812080949914269E-2f,
102 1.02643658689847095384E-1f,
103 -1.76416518357834055153E-1f,
104 2.52587186443633654823E-1f
108 /* Chebyshev coefficients for exp(-x) sqrt(x) I1(x)
109 * in the inverted interval [8,infinity].
111 * lim(x->inf){ exp(-x) sqrt(x) I1(x) } = 1/sqrt(2pi).
116 -3.83538038596423702205E-9f,
117 -2.63146884688951950684E-8f,
118 -2.51223623787020892529E-7f,
119 -3.88256480887769039346E-6f,
120 -1.10588938762623716291E-4f,
121 -9.76109749136146840777E-3f,
122 7.78576235018280120474E-1f
127 #define fabsf(x) ( (x) < 0 ? -(x) : (x) )
130 float chbevlf(float, float *, int);
131 float expf(float), sqrtf(float);
133 float chbevlf(), expf(), sqrtf();
151 z = chbevlf( y, A, 17 ) * z * expf(z);
155 z = expf(z) * chbevlf( 32.0f/z - 2.0f, B, 7 ) / sqrtf(z);
165 float i1ef( float xx )
178 z = chbevlf( y, A, 17 ) * z;
182 z = chbevlf( 32.0f/z - 2.0f, B, 7 ) / sqrtf(z);