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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; 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
              exception (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), log1p(3), sqrt(3)

COLOPHON

       This  page  is  part of release 3.23 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/.

                                  2008-08-10                            LOG(3)