function Mach=InversePrandtlMeyer(nu)% this coefficients and function was found from a file on internet
nu=nu*pi/180;
A=1.3604;
B=0.0962;
C=-0.5127;
D=-0.6722;
E=-0.3278;
nu_0=0.5*pi*(sqrt(6)-1);
y=(nu/nu_0)^(2/3);
Mach=(1 + A*y + B*y^2 + C*y^3)/(1 + D*y + E*y^2);
end