Originální popis anglicky:
lgamma, lgammaf, lgammal - log gamma function
Návod, kniha: POSIX Programmer's Manual
#include <math.h>
double lgamma(double
x);
float lgammaf(float
x);
long double lgammal(long double
x);
extern int signgam;
These functions shall compute
The argument
x need not be a non-positive integer (Gamma(x) is defined
over the reals, except the non-positive integers).
The sign of Gamma(x) is returned in the external integer
signgam.
These functions need not be reentrant. A function that is not required to be
reentrant is not required to be thread-safe.
An application wishing to check for error situations should set
errno to
zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these
functions. On return, if
errno is non-zero or
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
non-zero, an error has occurred.
Upon successful completion, these functions shall return the logarithmic gamma
of
x.
If
x is a non-positive integer, a pole error shall occur and
lgamma(),
lgammaf(), and
lgammal() shall return
+HUGE_VAL, +HUGE_VALF, and +HUGE_VALL, respectively.
If the correct value would cause overflow, a range error shall occur and
lgamma(),
lgammaf(), and
lgammal() shall return
±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (having the same
sign as the correct value), respectively.
If
x is NaN, a NaN shall be returned.
If
x is 1 or 2, +0 shall be returned.
If
x is ±Inf, +Inf shall be returned.
These functions shall fail if:
- Pole Error
- The x argument is a negative integer or zero.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero
floating-point exception shall be raised.
- Range Error
- The result overflows.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow
floating-point exception shall be raised.
The following sections are informative.
None.
On error, the expressions (math_errhandling & MATH_ERRNO) and
(math_errhandling & MATH_ERREXCEPT) are independent of each other, but at
least one of them must be non-zero.
None.
None.
exp() ,
feclearexcept() ,
fetestexcept() ,
isnan() ,
the Base Definitions volume of IEEE Std 1003.1-2001, Section
4.18, Treatment of Error Conditions for Mathematical Functions,
<math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
