double arspmfv(double g, double v);
Computes the mach number 
given the Prandtl-Meyer angle 
.
| Argument | Intent | Description |
| g | in | Specific heat constant |
| n | in | Prandtl-Meyer angle |
Return value
This function returns the mach number 
for the given mach Prandtl-Meyer angle 
or NAN (Not-a-Number) if an error has
occurred).
. 
.