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### 3. Library calls (functions within program libraries)

# CLOG

Section: Linux Programmer's Manual (3)

Updated: 2015-04-19

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## NAME

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

**#include <complex.h>**
## DESCRIPTION

These functions calculate the complex natural logarithm of
*z*,
with a branch cut along the negative real axis.
## 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 4.04 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
http://www.kernel.org/doc/man-pages/.

## Index

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Updated: 2015-04-19

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

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

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

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.

Interface | Attribute | Value |

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

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