man3/clog.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\"
   3 .\" SPDX-License-Identifier: GPL-1.0-or-later
   4 .\"
   5 .TH CLOG 3 2021-03-22 GNU "Linux Programmer's Manual"
   6 .SH NAME
   7 clog, clogf, clogl \- natural logarithm of a complex number
   8 .SH LIBRARY
   9 Math library
  10 .RI ( libm ", " \-lm )
  11 .SH SYNOPSIS
  12 .nf
  13 .B #include <complex.h>
  14 .PP
  15 .BI "double complex clog(double complex " z );
  16 .BI "float complex clogf(float complex " z );
  17 .BI "long double complex clogl(long double complex " z );
  18 .fi
  19 .SH DESCRIPTION
  20 These functions calculate the complex natural logarithm of
  21 .IR z ,
  22 with a branch cut along the negative real axis.
  23 .PP
  24 The logarithm
  25 .BR clog ()
  26 is the inverse function of the exponential
  27 .BR cexp (3).
  28 Thus, if \fIy\ =\ clog(z)\fP, then \fIz\ =\ cexp(y)\fP.
  29 The imaginary part of
  30 .I y
  31 is chosen in the interval [\-pi,pi].
  32 .PP
  33 One has:
  34 .PP
  35 .in +4n
  36 .EX
  37 clog(z) = log(cabs(z)) + I * carg(z)
  38 .EE
  39 .in
  40 .PP
  41 Note that
  42 .I z
  43 close to zero will cause an overflow.
  44 .SH VERSIONS
  45 These functions first appeared in glibc in version 2.1.
  46 .SH ATTRIBUTES
  47 For an explanation of the terms used in this section, see
  48 .BR attributes (7).
  49 .ad l
  50 .nh
  51 .TS
  52 allbox;
  53 lbx lb lb
  54 l l l.
  55 Interface       Attribute       Value
  56 T{
  57 .BR clog (),
  58 .BR clogf (),
  59 .BR clogl ()
  60 T}      Thread safety   MT-Safe
  61 .TE
  62 .hy
  63 .ad
  64 .sp 1
  65 .SH CONFORMING TO
  66 C99, POSIX.1-2001, POSIX.1-2008.
  67 .SH SEE ALSO
  68 .BR cabs (3),
  69 .BR cexp (3),
  70 .BR clog10 (3),
  71 .BR clog2 (3),
  72 .BR complex (7)