Returns the maximum numeric value of its arguments.
    This function is OpenVMS Alpha and Integrity servers only.
    Format
      #include  <math.h>
      double fmax  (double x, double y);
      float fmaxf  (float x, float y);
      long double fmaxl  (long double x, long double y);
1 – Argument
 x
    A real value.
 y
    A real value.
2 – Description
    The fmax functions determine the maximum numeric value of their
    arguments. NaN arguments are treated as missing data: if one
    argument is a NaN and the other numeric, then the numeric value
    is returned.
3 – Return Values
    n                  Upon success, the maximum numeric value of the
                       arguments. If just one argument is a NaN, the
                       other argument is returned.
    NaN                Both x and y are NaNs.