Help with commands to this problem

Hey guys, can someone help me? I have to solve two equations (bellow), Reynolds and the chord of an airfoil. But the chord depends on Cl ,Reynolds depends on the chord and Cl depends on Reynolds (an if command). How can I do that?

c = (8*pi*r/(B*CL)).*(1-cosd(phi));    
Re = ro*Vrel.*c./mi;
if Re < 3*10^4
            CL = 0.989;
            CD = 0.0151;
            alfa = 7,61;
        else 
            CL = 0.545;
            CD = 0.0081;
            alfa = 5.54;
end 

Answer 1

[Walter Roberson]

CL = 0.989 * ones(size(Re));
CD = 0.0151 * ones(size(Re));
alfa = 7.61 * ones(size(Re));   %not correction from 7,61

mask = Re >= 3E4;
CL(mask) = 0.545;
CD(mask) = 0.0081;
alfa(mask) = 5.54;

[Andressa Rosa]

Hey, thank you so much for helping me! It doesn't worked, Matlab doesn't recognize the variable CL in the other equation. Whenever I try to change the order one of them is not recognized.

[Walter Roberson]

?

You are defining c in terms of CL, and Re in terms of c, but if Re ends up being in a particular range then CL has to be a particular value and otherwise CL has to be another value??

If you designate any one of the variables B mi phi r ro Vrel as the independent variable, then it is possible to solve simultaneous equations to find the range on the designated independent variable that would need to be true in order for Re to be in the particular range, such as

-14835/(4*pi) < r

or

-8175/(4*pi) < r