3 * Modified Bessel function of order zero
17 * Returns modified Bessel function of order zero of the
20 * The function is defined as i0(x) = j0( 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 4.0e-7 7.9e-8
37 * Modified Bessel function of order zero,
38 * exponentially scaled
52 * Returns exponentially scaled modified Bessel function
53 * of order zero of the argument.
55 * The function is defined as i0e(x) = exp(-|x|) j0( ix ).
62 * arithmetic domain # trials peak rms
63 * IEEE 0,30 100000 3.7e-7 7.0e-8
72 Cephes Math Library Release 2.2: June, 1992
73 Copyright 1984, 1987, 1992 by Stephen L. Moshier
74 Direct inquiries to 30 Frost Street, Cambridge, MA 02140
79 /* Chebyshev coefficients for exp(-x) I0(x)
80 * in the interval [0,8].
82 * lim(x->0){ exp(-x) I0(x) } = 1.
87 -1.30002500998624804212E-8f,
88 6.04699502254191894932E-8f,
89 -2.67079385394061173391E-7f,
90 1.11738753912010371815E-6f,
91 -4.41673835845875056359E-6f,
92 1.64484480707288970893E-5f,
93 -5.75419501008210370398E-5f,
94 1.88502885095841655729E-4f,
95 -5.76375574538582365885E-4f,
96 1.63947561694133579842E-3f,
97 -4.32430999505057594430E-3f,
98 1.05464603945949983183E-2f,
99 -2.37374148058994688156E-2f,
100 4.93052842396707084878E-2f,
101 -9.49010970480476444210E-2f,
102 1.71620901522208775349E-1f,
103 -3.04682672343198398683E-1f,
104 6.76795274409476084995E-1f
108 /* Chebyshev coefficients for exp(-x) sqrt(x) I0(x)
109 * in the inverted interval [8,infinity].
111 * lim(x->inf){ exp(-x) sqrt(x) I0(x) } = 1/sqrt(2pi).
116 3.39623202570838634515E-9f,
117 2.26666899049817806459E-8f,
118 2.04891858946906374183E-7f,
119 2.89137052083475648297E-6f,
120 6.88975834691682398426E-5f,
121 3.36911647825569408990E-3f,
122 8.04490411014108831608E-1f
127 float chbevlf(float, float *, int), expf(float), sqrtf(float);
131 float chbevlf(), expf(), sqrtf();
144 return( expf(x) * chbevlf( y, A, 18 ) );
147 return( expf(x) * chbevlf( 32.0f/x - 2.0f, B, 7 ) / sqrtf(x) );
153 float chbevlf(float, float *, int), expf(float), sqrtf(float);
155 float i0ef( float x )
157 float chbevlf(), expf(), sqrtf();
170 return( chbevlf( y, A, 18 ) );
173 return( chbevlf( 32.0f/x - 2.0f, B, 7 ) / sqrtf(x) );