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COLOPHON

## NAME

## SYNOPSIS

## DESCRIPTION

## VERSIONS

## ATTRIBUTES

## CONFORMING TO

## SEE ALSO

## COLOPHON

SYNOPSIS

DESCRIPTION

VERSIONS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

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

**#include
<complex.h>**

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

long double complex clogl(long double complex

Link with
*−lm*.

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.

These functions first appeared in glibc in version 2.1.

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

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

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

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