### clog (3)

#### Leading comments

Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de) %%%LICENSE_START(GPL_NOVERSION_ONELINE) Distributed under GPL %%%LICENSE_END

#### 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)**.

Interface | Attribute | Value |

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

#### CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.#### SEE ALSO

**cabs(3)**,

**cexp(3)**,

**clog10(3)**,

**clog2(3)**,

**complex(7)**

#### COLOPHON

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