man3/clog.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\"
   3 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
   4 .\" Distributed under GPL
   5 .\" %%%LICENSE_END
   6 .\"
   7 .TH CLOG 3 2017-09-15 "" "Linux Programmer's Manual"
   8 .SH NAME
   9 clog, clogf, clogl \- natural logarithm of a complex number
  10 .SH SYNOPSIS
  11 .B #include <complex.h>
  12 .PP
  13 .BI "double complex clog(double complex " z );
  14 .br
  15 .BI "float complex clogf(float complex " z );
  16 .br
  17 .BI "long double complex clogl(long double complex " z );
  18 .PP
  19 Link with \fI\-lm\fP.
  20 .SH DESCRIPTION
  21 These functions calculate the complex natural logarithm of
  22 .IR z ,
  23 with a branch cut along the negative real axis.
  24 .PP
  25 The logarithm
  26 .BR clog ()
  27 is the inverse function of the exponential
  28 .BR cexp (3).
  29 Thus, if \fIy\ =\ clog(z)\fP, then \fIz\ =\ cexp(y)\fP.
  30 The imaginary part of
  31 .I y
  32 is chosen in the interval [\-pi,pi].
  33 .PP
  34 One has:
  35 .PP
  36 .nf
  37     clog(z) = log(cabs(z)) + I * carg(z)
  38 .fi
  39 .PP
  40 Note that
  41 .I z
  42 close to zero will cause an overflow.
  43 .SH VERSIONS
  44 These functions first appeared in glibc in version 2.1.
  45 .SH ATTRIBUTES
  46 For an explanation of the terms used in this section, see
  47 .BR attributes (7).
  48 .TS
  49 allbox;
  50 lbw24 lb lb
  51 l l l.
  52 Interface       Attribute       Value
  53 T{
  54 .BR clog (),
  55 .BR clogf (),
  56 .BR clogl ()
  57 T}      Thread safety   MT-Safe
  58 .TE
  59 .SH CONFORMING TO
  60 C99, POSIX.1-2001, POSIX.1-2008.
  61 .SH SEE ALSO
  62 .BR cabs (3),
  63 .BR cexp (3),
  64 .BR clog10 (3),
  65 .BR clog2 (3),
  66 .BR complex (7)