LOG1P
LOG1P
Section: Linux Programmer's Manual (3) Updated: 2010-09-20 Local index
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NAME
log1p, log1pf, log1pl - logarithm of 1 plus argument
SYNOPSIS
#include <math.h >
double log1p(double x );
float log1pf(float x );
long double log1pl(long double x );
Link with -lm .
Feature Test Macro Requirements for glibc (see
feature_test_macros (7)):

log1p ():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99
log1pf (),
log1pl ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99
DESCRIPTION
log1p(x)
returns a value equivalent to
log (1 + x )
It is computed in a way
that is accurate even if the value of x is near zero.
RETURN VALUE
On success, these functions return the natural logarithm of
(1 + x) .
If
x
is a NaN,
a NaN is returned.

If
x
is positive infinity, positive infinity is returned.

If
x
is -1, a pole error occurs,
and the functions return
-HUGE_VAL ,
-HUGE_VALF ,
or
-HUGE_VALL ,
respectively.

If
x
is less than -1 (including negative infinity),
a domain error occurs,
and a NaN (not a number) is returned.

ERRORS
See
math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
The following errors can occur:

Domain error: x is less than -1
An invalid floating-point exception
(FE_INVALID )
is raised.
Pole error: x is -1
A divide-by-zero floating-point exception
(FE_DIVBYZERO )
is raised.
These functions do not set
errno .

CONFORMING TO
C99, POSIX.1-2001.
SEE ALSO
exp (3),
expm1 (3),
log (3)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.

Index
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
SEE ALSO
COLOPHON
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Time: 21:49:36 GMT, April 16, 2011