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/* dlbeta.f -- translated by f2c (version 20041007).
You must link the resulting object file with libf2c:
on Microsoft Windows system, link with libf2c.lib;
on Linux or Unix systems, link with .../path/to/libf2c.a -lm
or, if you install libf2c.a in a standard place, with -lf2c -lm
-- in that order, at the end of the command line, as in
cc *.o -lf2c -lm
Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
http://www.netlib.org/f2c/libf2c.zip
*/
#define V3P_NETLIB_SRC
#include "v3p_netlib.h"
/* Table of constant values */
static integer c__1 = 1;
static integer c__2 = 2;
/* DECK DLBETA */
doublereal dlbeta_(doublereal *a, doublereal *b)
{
/* Initialized data */
static doublereal sq2pil = .91893853320467274178032973640562;
/* System generated locals */
doublereal ret_val, d__1;
/* Builtin functions */
double log(doublereal);
/* Local variables */
doublereal p, q, corr;
extern doublereal d9lgmc_(doublereal *), dgamma_(doublereal *), dlngam_(
doublereal *), dlnrel_(doublereal *);
extern /* Subroutine */ int xermsg_(char *, char *, char *, integer *,
integer *, ftnlen, ftnlen, ftnlen);
/* ***BEGIN PROLOGUE DLBETA */
/* ***PURPOSE Compute the natural logarithm of the complete Beta */
/* function. */
/* ***LIBRARY SLATEC (FNLIB) */
/* ***CATEGORY C7B */
/* ***TYPE DOUBLE PRECISION (ALBETA-S, DLBETA-D, CLBETA-C) */
/* ***KEYWORDS FNLIB, LOGARITHM OF THE COMPLETE BETA FUNCTION, */
/* SPECIAL FUNCTIONS */
/* ***AUTHOR Fullerton, W., (LANL) */
/* ***DESCRIPTION */
/* DLBETA(A,B) calculates the double precision natural logarithm of */
/* the complete beta function for double precision arguments */
/* A and B. */
/* ***REFERENCES (NONE) */
/* ***ROUTINES CALLED D9LGMC, DGAMMA, DLNGAM, DLNREL, XERMSG */
/* ***REVISION HISTORY (YYMMDD) */
/* 770701 DATE WRITTEN */
/* 890531 Changed all specific intrinsics to generic. (WRB) */
/* 890531 REVISION DATE from Version 3.2 */
/* 891214 Prologue converted to Version 4.0 format. (BAB) */
/* 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ) */
/* 900727 Added EXTERNAL statement. (WRB) */
/* ***END PROLOGUE DLBETA */
/* ***FIRST EXECUTABLE STATEMENT DLBETA */
p = min(*a,*b);
q = max(*a,*b);
if (p <= 0.) {
xermsg_("SLATEC", "DLBETA", "BOTH ARGUMENTS MUST BE GT ZERO", &c__1, &
c__2, (ftnlen)6, (ftnlen)6, (ftnlen)30);
}
if (p >= 10.) {
goto L30;
}
if (q >= 10.) {
goto L20;
}
/* P AND Q ARE SMALL. */
d__1 = p + q;
ret_val = log(dgamma_(&p) * (dgamma_(&q) / dgamma_(&d__1)));
return ret_val;
/* P IS SMALL, BUT Q IS BIG. */
L20:
d__1 = p + q;
corr = d9lgmc_(&q) - d9lgmc_(&d__1);
d__1 = -p / (p + q);
ret_val = dlngam_(&p) + corr + p - p * log(p + q) + (q - .5) * dlnrel_(&
d__1);
return ret_val;
/* P AND Q ARE BIG. */
L30:
d__1 = p + q;
corr = d9lgmc_(&p) + d9lgmc_(&q) - d9lgmc_(&d__1);
d__1 = -p / (p + q);
ret_val = log(q) * -.5 + sq2pil + corr + (p - .5) * log(p / (p + q)) + q *
dlnrel_(&d__1);
return ret_val;
} /* dlbeta_ */
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