clog(3) -- Linux man page
NAMEclog, clogf, clogl - natural logarithm of a complex number
double complex clog(double complexz);
float complex clogf(float complex z);
long double complex clogl(long double complexz);
DESCRIPTIONThe 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 [-I*pi,I*pi].
One has clog(z) = log(cabs(z))+I*carg(z).