clog - Man Page

natural logarithm of a complex number


Math library (libm, -lm)


#include <complex.h>

double complex clog(double complex z);
float complex clogf(float complex z);
long double complex clogl(long double complex z);


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.


These functions first appeared in glibc in version 2.1.


For an explanation of the terms used in this section, see attributes(7).

clog(), clogf(), clogl()Thread safetyMT-Safe


C99, POSIX.1-2001, POSIX.1-2008.

See Also

cabs(3), cexp(3), clog10(3), clog2(3), complex(7)

Referenced By

cacos(3), casin(3), catan(3), cexp(3), clog10(3), clog2(3), complex(7), log(3).

The man pages clogf(3) and clogl(3) are aliases of clog(3).

2022-10-09 Linux man-pages 6.01