# clog (3) - Linux Manuals

## clog: natural logarithm of a complex number

## 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***);**

## 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).

Interface | Attribute | Value |

clog(),
clogf(),
clogl()
| Thread safety | MT-Safe |

## CONFORMING TO

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

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