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/* d9gmit.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__1 = 1;
static integer c__2 = 2;
static doublereal c_b19 = 1.;
/* DECK D9GMIT */
doublereal d9gmit_(doublereal *a, doublereal *x, doublereal *algap1,
doublereal *sgngam, doublereal *alx)
{
/* Initialized data */
// static logical first = TRUE_;
/* System generated locals */
integer i__1;
doublereal ret_val, d__1;
/* Builtin functions */
double log(doublereal), d_sign(doublereal *, doublereal *), exp(
doublereal);
/* Local variables */
integer k, m;
doublereal s, t, ae;
integer ma;
doublereal fk, te;
/* static */ doublereal bot, eps;
doublereal alg2, algs = 0.0, aeps, sgng2;
extern doublereal d1mach_(integer *), dlngam_(doublereal *);
extern /* Subroutine */ int xermsg_(char *, char *, char *, integer *,
integer *, ftnlen, ftnlen, ftnlen);
/* ***BEGIN PROLOGUE D9GMIT */
/* ***SUBSIDIARY */
/* ***PURPOSE Compute Tricomi's incomplete Gamma function for small */
/* arguments. */
/* ***LIBRARY SLATEC (FNLIB) */
/* ***CATEGORY C7E */
/* ***TYPE DOUBLE PRECISION (R9GMIT-S, D9GMIT-D) */
/* ***KEYWORDS COMPLEMENTARY INCOMPLETE GAMMA FUNCTION, FNLIB, SMALL X, */
/* SPECIAL FUNCTIONS, TRICOMI */
/* ***AUTHOR Fullerton, W., (LANL) */
/* ***DESCRIPTION */
/* Compute Tricomi's incomplete gamma function for small X. */
/* ***REFERENCES (NONE) */
/* ***ROUTINES CALLED D1MACH, DLNGAM, XERMSG */
/* ***REVISION HISTORY (YYMMDD) */
/* 770701 DATE WRITTEN */
/* 890531 Changed all specific intrinsics to generic. (WRB) */
/* 890911 Removed unnecessary intrinsics. (WRB) */
/* 890911 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 D9GMIT */
/* ***FIRST EXECUTABLE STATEMENT D9GMIT */
// d1mach has been made thread safe, so there is no need for the
// statics in determining eps and bot
// if (first) {
// eps = d1mach_(&c__3) * .5;
// bot = log(d1mach_(&c__1));
// }
// first = FALSE_;
eps = d1mach_(&c__3) * .5;
bot = log(d1mach_(&c__1));
if (*x <= 0.) {
xermsg_("SLATEC", "D9GMIT", "X SHOULD BE GT 0", &c__1, &c__2, (ftnlen)
6, (ftnlen)6, (ftnlen)16);
}
ma = (integer) (*a + .5);
if (*a < 0.) {
ma = (integer) (*a - .5);
}
aeps = *a - ma;
ae = *a;
if (*a < -.5) {
ae = aeps;
}
t = 1.;
te = ae;
s = t;
for (k = 1; k <= 200; ++k) {
fk = (doublereal) k;
te = -(*x) * te / fk;
t = te / (ae + fk);
s += t;
if (abs(t) < eps * abs(s)) {
goto L30;
}
/* L20: */
}
xermsg_("SLATEC", "D9GMIT", "NO CONVERGENCE IN 200 TERMS OF TAYLOR-S SER"
"IES", &c__2, &c__2, (ftnlen)6, (ftnlen)6, (ftnlen)46);
L30:
if (*a >= -.5) {
algs = -(*algap1) + log(s);
}
if (*a >= -.5) {
goto L60;
}
d__1 = aeps + 1.;
algs = -dlngam_(&d__1) + log(s);
s = 1.;
m = -ma - 1;
if (m == 0) {
goto L50;
}
t = 1.;
i__1 = m;
for (k = 1; k <= i__1; ++k) {
t = *x * t / (aeps - (m + 1 - k));
s += t;
if (abs(t) < eps * abs(s)) {
goto L50;
}
/* L40: */
}
L50:
ret_val = 0.;
algs = -ma * log(*x) + algs;
if (s == 0. || aeps == 0.) {
goto L60;
}
sgng2 = *sgngam * d_sign(&c_b19, &s);
alg2 = -(*x) - *algap1 + log((abs(s)));
if (alg2 > bot) {
ret_val = sgng2 * exp(alg2);
}
if (algs > bot) {
ret_val += exp(algs);
}
return ret_val;
L60:
ret_val = exp(algs);
return ret_val;
} /* d9gmit_ */
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