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/* dgamit.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__1 = 1;
static integer c__2 = 2;
static doublereal c_b10 = 1.;
/* DECK DGAMIT */
doublereal dgamit_(doublereal *a, doublereal *x)
{
/* Initialized data */
// static logical first = TRUE_;
/* System generated locals */
doublereal ret_val, d__1, d__2;
/* Builtin functions */
double log(doublereal), sqrt(doublereal), d_sign(doublereal *, doublereal
*), d_int(doublereal *), exp(doublereal);
/* Local variables */
doublereal h__, t, sga, alx;
/* static */ doublereal bot;
doublereal alng, aeps;
extern doublereal dgamr_(doublereal *);
doublereal ainta;
/* static */ doublereal sqeps;
extern doublereal d1mach_(integer *);
doublereal algap1;
extern doublereal d9lgic_(doublereal *, doublereal *, doublereal *),
d9lgit_(doublereal *, doublereal *, doublereal *), d9gmit_(
doublereal *, doublereal *, doublereal *, doublereal *,
doublereal *), dlngam_(doublereal *);
extern /* Subroutine */ int dlgams_(doublereal *, doublereal *,
doublereal *);
doublereal sgngam;
/* static */ doublereal alneps;
// extern /* Subroutine */ int xerclr_(void);
extern /* Subroutine */ int xermsg_(char *, char *, char *,
integer *, integer *, ftnlen, ftnlen, ftnlen);
/* ***BEGIN PROLOGUE DGAMIT */
/* ***PURPOSE Calculate Tricomi's form of the incomplete Gamma function. */
/* ***LIBRARY SLATEC (FNLIB) */
/* ***CATEGORY C7E */
/* ***TYPE DOUBLE PRECISION (GAMIT-S, DGAMIT-D) */
/* ***KEYWORDS COMPLEMENTARY INCOMPLETE GAMMA FUNCTION, FNLIB, */
/* SPECIAL FUNCTIONS, TRICOMI */
/* ***AUTHOR Fullerton, W., (LANL) */
/* ***DESCRIPTION */
/* Evaluate Tricomi's incomplete Gamma function defined by */
/* DGAMIT = X**(-A)/GAMMA(A) * integral from 0 to X of EXP(-T) * */
/* T**(A-1.) */
/* for A .GT. 0.0 and by analytic continuation for A .LE. 0.0. */
/* GAMMA(X) is the complete gamma function of X. */
/* DGAMIT is evaluated for arbitrary real values of A and for non- */
/* negative values of X (even though DGAMIT is defined for X .LT. */
/* 0.0), except that for X = 0 and A .LE. 0.0, DGAMIT is infinite, */
/* which is a fatal error. */
/* The function and both arguments are DOUBLE PRECISION. */
/* A slight deterioration of 2 or 3 digits accuracy will occur when */
/* DGAMIT is very large or very small in absolute value, because log- */
/* arithmic variables are used. Also, if the parameter A is very */
/* close to a negative integer (but not a negative integer), there is */
/* a loss of accuracy, which is reported if the result is less than */
/* half machine precision. */
/* ***REFERENCES W. Gautschi, A computational procedure for incomplete */
/* gamma functions, ACM Transactions on Mathematical */
/* Software 5, 4 (December 1979), pp. 466-481. */
/* W. Gautschi, Incomplete gamma functions, Algorithm 542, */
/* ACM Transactions on Mathematical Software 5, 4 */
/* (December 1979), pp. 482-489. */
/* ***ROUTINES CALLED D1MACH, D9GMIT, D9LGIC, D9LGIT, DGAMR, DLGAMS, */
/* DLNGAM, XERCLR, 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) */
/* 920528 DESCRIPTION and REFERENCES sections revised. (WRB) */
/* ***END PROLOGUE DGAMIT */
/* ***FIRST EXECUTABLE STATEMENT DGAMIT */
// d1mach has been made thread safe, so there is no need for the
// statics in determining these values
// if (first) {
// alneps = -log(d1mach_(&c__3));
// sqeps = sqrt(d1mach_(&c__4));
// bot = log(d1mach_(&c__1));
// }
// first = FALSE_;
alneps = -log(d1mach_(&c__3));
sqeps = sqrt(d1mach_(&c__4));
bot = log(d1mach_(&c__1));
if (*x < 0.) {
xermsg_("SLATEC", "DGAMIT", "X IS NEGATIVE", &c__2, &c__2, (ftnlen)6,
(ftnlen)6, (ftnlen)13);
}
if (*x != 0.) {
alx = log(*x);
}
sga = 1.;
if (*a != 0.) {
sga = d_sign(&c_b10, a);
}
d__1 = *a + sga * .5;
ainta = d_int(&d__1);
aeps = *a - ainta;
if (*x > 0.) {
goto L20;
}
ret_val = 0.;
if (ainta > 0. || aeps != 0.) {
d__1 = *a + 1.;
ret_val = dgamr_(&d__1);
}
return ret_val;
L20:
if (*x > 1.) {
goto L30;
}
if (*a >= -.5 || aeps != 0.) {
d__1 = *a + 1.;
dlgams_(&d__1, &algap1, &sgngam);
}
ret_val = d9gmit_(a, x, &algap1, &sgngam, &alx);
return ret_val;
L30:
if (*a < *x) {
goto L40;
}
d__2 = *a + 1.;
d__1 = dlngam_(&d__2);
t = d9lgit_(a, x, &d__1);
if (t < bot) {
// xerclr_();
}
ret_val = exp(t);
return ret_val;
L40:
alng = d9lgic_(a, x, &alx);
/* EVALUATE DGAMIT IN TERMS OF LOG (DGAMIC (A, X)) */
h__ = 1.;
if (aeps == 0. && ainta <= 0.) {
goto L50;
}
d__1 = *a + 1.;
dlgams_(&d__1, &algap1, &sgngam);
t = log((abs(*a))) + alng - algap1;
if (t > alneps) {
goto L60;
}
if (t > -alneps) {
h__ = 1. - sga * sgngam * exp(t);
}
if (abs(h__) > sqeps) {
goto L50;
}
// xerclr_();
xermsg_("SLATEC", "DGAMIT", "RESULT LT HALF PRECISION", &c__1, &c__1, (
ftnlen)6, (ftnlen)6, (ftnlen)24);
L50:
t = -(*a) * alx + log((abs(h__)));
if (t < bot) {
// xerclr_();
}
d__1 = exp(t);
ret_val = d_sign(&d__1, &h__);
return ret_val;
L60:
t -= *a * alx;
if (t < bot) {
// xerclr_();
}
ret_val = -sga * sgngam * exp(t);
return ret_val;
} /* dgamit_ */
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