gamma.3m

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)gamma.3m	6.3	8/30/89
.\"
.TH gamma 3m RISC
.ds nn \fINaN\fR
.SH Name
gamma, lgamma, signgam \- log gamma function
.SH Syntax
.nf
.B #include <math.h>
.PP
.B double gamma(\fIx\fP)
.B double \fIx\fP;
.PP
.B double lgamma(\fIx\fP)
.B double \fIx\fP;
.PP
.fi
.B extern int
.PN signgam;
.SH Description
The
.PN gamma
.NXR "gamma subroutine"
.NXR "gamma function"
function returns ln \||\|\(*G(\||\|\fIx\fR\||\|)\||\|.
The sign of \(*G(\||\|\fIx\fR\||\|) is returned in the external integer
.PN signgam .
The following C program might be used to calculate \(*G:
.PP
.EX
y = gamma(\fIx\fP);
if (y > 88.0)
	error();
y = exp(y);
if(signgam)
	y = \-y;
.EE
.PP
The
.PN lgamma
function is another name for the
.PN gamma
function.
.SH Return Values
The
.PN gamma
and
.PN lgamma
functions return \*(nn when
.I x
is \*(nn or when it
is an integer value less than or equal to zero.  On overflow
.PN gamma
and
.PN lgamma
functions return HUGE_VAL.
.SH Environment
When your program is compiled using the 
System V environment for nonpositive integer
values, HUGE is returned, and 
.I errno
is set to EDOM.  
A message indicating DOMAIN error is 
printed on the standard error output.
.PP
If the correct value would overflow, 
.PN gamma
returns HUGE and sets
.I errno
to ERANGE.
.PP
These error-handling procedures may be changed with the function
.MS matherr 3m .
.SH See Also
matherr(3m)