# CLOG

NAME

SYNOPSIS

DESCRIPTION

VERSIONS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## NAME

clog, clogf,
clogl - natural logarithm of a complex number

## SYNOPSIS

**#include
<complex.h>**

**double
complex clog(double complex** *z***); **

float complex clogf(float complex *z***); **

long double complex clogl(long double complex
*z***);**

Link with
*-lm*.

## DESCRIPTION

These functions
calculate the complex natural logarithm of *z*, with a
branch cut along the negative real axis.

The logarithm
**clog**() is the inverse function of the exponential
**cexp**(3). Thus, if *y = clog(z)*, then
*z = cexp(y)*. The imaginary part of *y*
is chosen in the interval [-pi,pi].

One has:

clog(z) =
log(cabs(z)) + I * carg(z)

Note that
*z* close to zero will cause an overflow.

## VERSIONS

These functions
first appeared in glibc in version 2.1.

## ATTRIBUTES

For an
explanation of the terms used in this section, see
**attributes**(7).

## CONFORMING TO

C99,
POSIX.1-2001, POSIX.1-2008.

## SEE ALSO

**cabs**(3),
**cexp**(3), **clog10**(3), **clog2**(3),
**complex**(7)

## COLOPHON

This page is
part of release 4.15 of the Linux *man-pages* project.
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/.