3 * Modified Bessel function, third kind, order zero
17 * Returns modified Bessel function of the third kind
18 * of order zero of the argument.
20 * The range is partitioned into the two intervals [0,8] and
21 * (8, infinity). Chebyshev polynomial expansions are employed
28 * Tested at 2000 random points between 0 and 8. Peak absolute
29 * error (relative when K0 > 1) was 1.46e-14; rms, 4.26e-15.
31 * arithmetic domain # trials peak rms
32 * IEEE 0, 30 30000 7.8e-7 8.5e-8
36 * message condition value returned
37 * K0 domain x <= 0 MAXNUM
42 * Modified Bessel function, third kind, order zero,
43 * exponentially scaled
57 * Returns exponentially scaled modified Bessel function
58 * of the third kind of order zero of the argument.
65 * arithmetic domain # trials peak rms
66 * IEEE 0, 30 30000 8.1e-7 7.8e-8
72 Cephes Math Library Release 2.0: April, 1987
73 Copyright 1984, 1987 by Stephen L. Moshier
74 Direct inquiries to 30 Frost Street, Cambridge, MA 02140
79 /* Chebyshev coefficients for K0(x) + log(x/2) I0(x)
80 * in the interval [0,2]. The odd order coefficients are all
81 * zero; only the even order coefficients are listed.
83 * lim(x->0){ K0(x) + log(x/2) I0(x) } = -EUL.
88 1.90451637722020886025E-9f,
89 2.53479107902614945675E-7f,
90 2.28621210311945178607E-5f,
91 1.26461541144692592338E-3f,
92 3.59799365153615016266E-2f,
93 3.44289899924628486886E-1f,
94 -5.35327393233902768720E-1f
99 /* Chebyshev coefficients for exp(x) sqrt(x) K0(x)
100 * in the inverted interval [2,infinity].
102 * lim(x->inf){ exp(x) sqrt(x) K0(x) } = sqrt(pi/2).
106 -1.69753450938905987466E-9f,
107 8.57403401741422608519E-9f,
108 -4.66048989768794782956E-8f,
109 2.76681363944501510342E-7f,
110 -1.83175552271911948767E-6f,
111 1.39498137188764993662E-5f,
112 -1.28495495816278026384E-4f,
113 1.56988388573005337491E-3f,
114 -3.14481013119645005427E-2f,
115 2.44030308206595545468E0f
120 extern float MAXNUMF;
123 float chbevlf(float, float *, int);
124 float expf(float), i0f(float), logf(float), sqrtf(float);
126 float chbevlf(), expf(), i0f(), logf(), sqrtf();
131 float k0f( float xx )
142 mtherr( "k0f", DOMAIN );
149 y = chbevlf( y, A, 7 ) - logf( 0.5f * x ) * i0f(x);
153 y = expf(-x) * chbevlf( z, B, 10 ) / sqrtf(x);
160 float k0ef( float xx )
172 mtherr( "k0ef", DOMAIN );
179 y = chbevlf( y, A, 7 ) - logf( 0.5f * x ) * i0f(x);
180 return( y * expf(x) );
183 y = chbevlf( 8.0f/x - 2.0f, B, 10 ) / sqrtf(x);