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  • sasmodels/models/lib/j0_cephes.c

    rbfef528 r094e320  
    4444 */ 
    4545 
    46 /*                                                      y0.c 
    47  * 
    48  *      Bessel function of the second kind, order zero 
    49  * 
    50  * 
    51  * 
    52  * SYNOPSIS: 
    53  * 
    54  * double x, y, y0(); 
    55  * 
    56  * y = y0( x ); 
    57  * 
    58  * 
    59  * 
    60  * DESCRIPTION: 
    61  * 
    62  * Returns Bessel function of the second kind, of order 
    63  * zero, of the argument. 
    64  * 
    65  * The domain is divided into the intervals [0, 5] and 
    66  * (5, infinity). In the first interval a rational approximation 
    67  * R(x) is employed to compute 
    68  *   y0(x)  = R(x)  +   2 * log(x) * j0(x) / PI. 
    69  * Thus a call to j0() is required. 
    70  * 
    71  * In the second interval, the Hankel asymptotic expansion 
    72  * is employed with two rational functions of degree 6/6 
    73  * and 7/7. 
    74  * 
    75  * 
    76  * 
    77  * ACCURACY: 
    78  * 
    79  *  Absolute error, when y0(x) < 1; else relative error: 
    80  * 
    81  * arithmetic   domain     # trials      peak         rms 
    82  *    DEC       0, 30        9400       7.0e-17     7.9e-18 
    83  *    IEEE      0, 30       30000       1.3e-15     1.6e-16 
    84  * 
    85  */ 
    86  
    8746 
    8847/* 
    … …  
    9554 
    9655double j0( double ); 
    97  
    9856double j0(double x) { 
    9957 
    … …  
    291249 
    292250    q = 1.0/x; 
    293     w = sqrtf(q); 
     251    w = sqrt(q); 
    294252 
    295253    p = w * polevl( q, MO, 7); 
    296254    w = q*q; 
    297255    xn = q * polevl( w, PH, 7) - PIO4F; 
    298     p = p * cosf(xn + xx); 
     256    p = p * cos(xn + xx); 
    299257    return(p); 
    300258#endif 
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