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LOG(3)                     Linux Programmer's Manual                    LOG(3)

NAME
       log, logf, logl - natural logarithmic function
SYNOPSIS
       #include <math.h>
       double log(double x);
       float logf(float x);
       long double logl(long double x);
       Link with -lm.
   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
       logf(), logl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99
DESCRIPTION
       The log() function returns the natural logarithm of x.
RETURN VALUE
       On success, these functions return the natural logarithm of x.
       If x is a NaN, a NaN is returned.
       If x is 1, the result is +0.
       If x is positive infinity, positive infinity is returned.
       If x is zero, then a  pole  error  occurs,  and  the  functions  return
       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
       If  x  is  negative  (including negative infinity), then 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 negative
              errno  is  set  to  EDOM.   An  invalid floating-point exception
              (FE_INVALID) is raised.
       Pole error: x is zero
              errno is set to ERANGE.  A divide-by-zero floating-point  excep-
              tion (FE_DIVBYZERO) is raised.
CONFORMING TO
       C99, POSIX.1-2001.  The variant returning double also conforms to SVr4,
       4.3BSD, C89.
BUGS
       In glibc 2.5 and earlier, taking the log() of a NaN  produces  a  bogus
       invalid floating-point (FE_INVALID) exception.
SEE ALSO
       cbrt(3), clog(3), log10(3), log1p(3), log2(3), sqrt(3)
COLOPHON
       This  page  is  part of release 3.53 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/.

                                  2010-09-20                            LOG(3)