void arfitf(double g, double l, bool is_sub, double result[6], int *ierr);
Compute the isothermal relations given the characteristic line, 
.
| Argument | Intent | Description |
| g | in | Specific heat constant |
| l | in | Characteristic line |
| is_sub | in | Whether |
| result | out | Array with result properties as described in 6. |
| ierr | out | (optional) Return status code |
Specific heat ratio 
.
Computed 
out of range.
Given 
out of range.
Iterative solver failed.
. 
. 
corresponding to the given 
is assumed to be
sub- or super- sonic.