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/* d9lgit.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
*/
/** This routine has been editted to be thread safe **/
#define V3P_NETLIB_SRC
#include "v3p_netlib.h"
/* Table of constant values */
static integer c__3 = 3;
static integer c__4 = 4;
static integer c__2 = 2;
static integer c__1 = 1;
/* DECK D9LGIT */
doublereal d9lgit_(doublereal *a, doublereal *x, doublereal *algap1)
{
/* Initialized data */
// static logical first = TRUE_;
/* System generated locals */
doublereal ret_val;
/* Builtin functions */
double sqrt(doublereal), log(doublereal);
/* Local variables */
integer k;
doublereal p, r__, s, t, fk, ax, a1x;
/* static */ doublereal eps;
doublereal hstar;
/* static */ doublereal sqeps;
extern doublereal d1mach_(integer *);
extern /* Subroutine */ int xermsg_(char *, char *, char *, integer *,
integer *, ftnlen, ftnlen, ftnlen);
/* ***BEGIN PROLOGUE D9LGIT */
/* ***SUBSIDIARY */
/* ***PURPOSE Compute the logarithm of Tricomi's incomplete Gamma */
/* function with Perron's continued fraction for large X and */
/* A .GE. X. */
/* ***LIBRARY SLATEC (FNLIB) */
/* ***CATEGORY C7E */
/* ***TYPE DOUBLE PRECISION (R9LGIT-S, D9LGIT-D) */
/* ***KEYWORDS FNLIB, INCOMPLETE GAMMA FUNCTION, LOGARITHM, */
/* PERRON'S CONTINUED FRACTION, SPECIAL FUNCTIONS, TRICOMI */
/* ***AUTHOR Fullerton, W., (LANL) */
/* ***DESCRIPTION */
/* Compute the log of Tricomi's incomplete gamma function with Perron's */
/* continued fraction for large X and for A .GE. X. */
/* ***REFERENCES (NONE) */
/* ***ROUTINES CALLED D1MACH, 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) */
/* 900720 Routine changed from user-callable to subsidiary. (WRB) */
/* ***END PROLOGUE D9LGIT */
/* ***FIRST EXECUTABLE STATEMENT D9LGIT */
// d1mach has been made thread safe, so there is no need for the
// statics in determining eps and sqeps
// if (first) {
// eps = d1mach_(&c__3) * .5;
// sqeps = sqrt(d1mach_(&c__4));
// }
// first = FALSE_;
eps = d1mach_(&c__3) * .5;
sqeps = sqrt(d1mach_(&c__4));
if (*x <= 0. || *a < *x) {
xermsg_("SLATEC", "D9LGIT", "X SHOULD BE GT 0.0 AND LE A", &c__2, &
c__2, (ftnlen)6, (ftnlen)6, (ftnlen)27);
}
ax = *a + *x;
a1x = ax + 1.;
r__ = 0.;
p = 1.;
s = p;
for (k = 1; k <= 200; ++k) {
fk = (doublereal) k;
t = (*a + fk) * *x * (r__ + 1.);
r__ = t / ((ax + fk) * (a1x + fk) - t);
p = r__ * p;
s += p;
if (abs(p) < eps * s) {
goto L30;
}
/* L20: */
}
xermsg_("SLATEC", "D9LGIT", "NO CONVERGENCE IN 200 TERMS OF CONTINUED FR"
"ACTION", &c__3, &c__2, (ftnlen)6, (ftnlen)6, (ftnlen)49);
L30:
hstar = 1. - *x * s / a1x;
if (hstar < sqeps) {
xermsg_("SLATEC", "D9LGIT", "RESULT LESS THAN HALF PRECISION", &c__1,
&c__1, (ftnlen)6, (ftnlen)6, (ftnlen)31);
}
ret_val = -(*x) - *algap1 - log(hstar);
return ret_val;
} /* d9lgit_ */
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