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/* dgami.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 DGAMI */
doublereal dgami_(doublereal *a, doublereal *x)
{
/* System generated locals */
doublereal ret_val;
/* Builtin functions */
double log(doublereal), exp(doublereal);
/* Local variables */
extern doublereal dlngam_(doublereal *), dgamit_(doublereal *, doublereal
*);
doublereal factor;
extern /* Subroutine */ int xermsg_(char *, char *, char *, integer *,
integer *, ftnlen, ftnlen, ftnlen);
/* ***BEGIN PROLOGUE DGAMI */
/* ***PURPOSE Evaluate the incomplete Gamma function. */
/* ***LIBRARY SLATEC (FNLIB) */
/* ***CATEGORY C7E */
/* ***TYPE DOUBLE PRECISION (GAMI-S, DGAMI-D) */
/* ***KEYWORDS FNLIB, INCOMPLETE GAMMA FUNCTION, SPECIAL FUNCTIONS */
/* ***AUTHOR Fullerton, W., (LANL) */
/* ***DESCRIPTION */
/* Evaluate the incomplete gamma function defined by */
/* DGAMI = integral from T = 0 to X of EXP(-T) * T**(A-1.0) . */
/* DGAMI is evaluated for positive values of A and non-negative values */
/* of X. A slight deterioration of 2 or 3 digits accuracy will occur */
/* when DGAMI is very large or very small, because logarithmic variables */
/* are used. The function and both arguments are double precision. */
/* ***REFERENCES (NONE) */
/* ***ROUTINES CALLED DGAMIT, DLNGAM, 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) */
/* ***END PROLOGUE DGAMI */
/* ***FIRST EXECUTABLE STATEMENT DGAMI */
if (*a <= 0.) {
xermsg_("SLATEC", "DGAMI", "A MUST BE GT ZERO", &c__1, &c__2, (ftnlen)
6, (ftnlen)5, (ftnlen)17);
}
if (*x < 0.) {
xermsg_("SLATEC", "DGAMI", "X MUST BE GE ZERO", &c__2, &c__2, (ftnlen)
6, (ftnlen)5, (ftnlen)17);
}
ret_val = 0.;
if (*x == 0.) {
return ret_val;
}
/* THE ONLY ERROR POSSIBLE IN THE EXPRESSION BELOW IS A FATAL OVERFLOW. */
factor = exp(dlngam_(a) + *a * log(*x));
ret_val = factor * dgamit_(a, x);
return ret_val;
} /* dgami_ */
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