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'\" t
.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.TH clog 3 2023-10-31 "Linux man-pages 6.7"
.SH NAME
clog, clogf, clogl \- natural logarithm of a complex number
.SH LIBRARY
Math library
.RI ( libm ", " \-lm )
.SH SYNOPSIS
.nf
.B #include <complex.h>
.P
.BI "double complex clog(double complex " z );
.BI "float complex clogf(float complex " z );
.BI "long double complex clogl(long double complex " z );
.fi
.SH DESCRIPTION
These functions calculate the complex natural logarithm of
.IR z ,
with a branch cut along the negative real axis.
.P
The logarithm
.BR clog ()
is the inverse function of the exponential
.BR cexp (3).
Thus, if \fIy\ =\ clog(z)\fP, then \fIz\ =\ cexp(y)\fP.
The imaginary part of
.I y
is chosen in the interval [\-pi,pi].
.P
One has:
.P
.in +4n
.EX
clog(z) = log(cabs(z)) + I * carg(z)
.EE
.in
.P
Note that
.I z
close to zero will cause an overflow.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR clog (),
.BR clogf (),
.BR clogl ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
glibc 2.1.
C99, POSIX.1-2001.
.SH SEE ALSO
.BR cabs (3),
.BR cexp (3),
.BR clog10 (3),
.BR clog2 (3),
.BR complex (7)
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