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**NAME**

log, logf, logl - natural logarithmic function

**SYNOPSIS**

#include<math.h>doublelog(doublex);floatlogf(floatx);longdoublelogl(longdoublex);Link with-lm. Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):logf(),logl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

**DESCRIPTION**

These functions return the natural logarithm ofx.

**RETURN** **VALUE**

On success, these functions return the natural logarithm ofx. Ifxis a NaN, a NaN is returned. Ifxis 1, the result is +0. Ifxis positive infinity, positive infinity is returned. Ifxis zero, then a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively. Ifxis negative (including negative infinity), then a domain error occurs, and a NaN (not a number) is returned.

**ERRORS**

Seemath_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur: Domain error:xis negativeerrnois set toEDOM. An invalid floating-point exception (FE_INVALID) is raised. Pole error:xis zeroerrnois set toERANGE. A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

**ATTRIBUTES**

For an explanation of the terms used in this section, seeattributes(7). ┌──────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├──────────────────────┼───────────────┼─────────┤ │log(),logf(),logl() │ Thread safety │ MT-Safe │ └──────────────────────┴───────────────┴─────────┘

**CONFORMING** **TO**

C99, POSIX.1-2001, POSIX.1-2008. The variant returningdoublealso conforms to SVr4, 4.3BSD, C89.

**BUGS**

In glibc 2.5 and earlier, taking thelog() 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 5.10 of the Linuxman-pagesproject. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15 LOG(3)