Returns the complex hyperbolic tangent of its argument.
    This function is OpenVMS Alpha and Integrity servers only.
    Format
      #include  <complex.h>
      double complex ctanh  (double complex z);
      float complex ctanhf  (float complex z);
      long double complex ctanhl  (long double complex z);
1 – Argument
 z
    A complex value.
2 – Description
    The ctanh functions compute the complex hyperbolic tangent value
    of z.
3 – Return Values
x The complex hyperbolic tangent value.