# clogf (3)

# 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)