Compute the complex natural (base-e) logarithm of a complex number
#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 compute the complex natural (base-e) logarithm of the complex number specified by z with a branch cut along the negative real axis. The natural logarithm of a complex number z with polar coordinate components (r,θ) equals ln r + i(θ+2nπ), with the principal value ln r + iθ.
To check for error situations, use feclearexcept() and fetestexcept(). For example:
If no errors occur, the complex natural logarithm of z, in the range of a strip in the interval [−iπ, +iπ] along the imaginary axis and mathematically unbounded along the real axis.
| If z is: | These functions return: | Errors: |
|---|---|---|
| -0 + 0i | -Inf + πi | FE_DIVBYZERO |
| 0 + 0i | -Inf + 0i | FE_DIVBYZERO |
| x + Infi, for any finite x | Inf + (π/2)i | — |
| x + NaNi, for any finite x | NaN + NaNi | — |
| -Inf + yi, for any finite positive y | -Inf + πi | — |
| Inf + yi, for any finite positive y | -Inf + 0i | — |
| -Inf + Infi | Inf + (3π/4)i | — |
| Inf + Infi | Inf + (π/4)i | — |
| ±Inf + NaNi | NaN + NaNi | — |
| NaN + yi, for any finite y | NaN + NaNi | — |
| NaN + Infi | NaN + NaNi | — |
| NaN + NaNi | NaN + NaNi | — |
These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | No |
| Signal handler | No |
| Thread | Yes |