Returns the complex natural (base e) logarithm of its argument.
    This function is OpenVMS Alpha and Integrity servers only.
    Format
      #include  <complex.h>
      double complex clog  (double complex z);
      float complex clogf  (float complex z);
      long double complex clogl  (long double complex z);
1 – Argument
 z
    A complex value.
2 – Description
    The clog functions return the complex natural (base e) logarithm
    of z, with a branch cut along the negative real axis.
3 – Return Values
    x                  The complex natural logarithm value in the
                       range of a strip mathematically unbounded
                       along the real axis and in the interval [-
                       iπ, +iπ] along the imaginary axis.