015o_clog.asciidoc

clog

NAME

clog - 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);

CONFORMING TO

C99

DESCRIPTION

The logarithm clog() is the inverse function of the exponential cexp(). 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.

RETURN VALUE

Returns the complex natural logarithm in the range of a strip mathematically unbound along the real axis and in the interval [-I*pi,I*pi] along the imaginary axis.

SEE ALSO

cexp, cabs, clog10, clog2, complex

EXAMPLE

link:src/clog.c[role=include]

OUTPUT

$ gcc -Wall -lm clog.c
$ ./a.out
2*log(i) = 0.0+3.141593i
4*log(sqrt(2)/2+sqrt(2)i/2) = 0.0+3.141593i
log(-1+0i) = 0.0+3.141593i
log(-1-0i) (the other side of the cut) = 0.0-3.141593i