Trouble with while loop

Hello,

I'm having trouble fixing the while loop. The idea is to increment x while the error is larger than 1%, the loop doesn't seem to stop and outputs a very large value for the error (2e6). Everything is running smoothly until I reach the part where I have to compare Pb_calc to Pb and im not sure how to loop over them.

Thank you

k=1.4;
A_throat =  1.0841e+03;
r_throat = sqrt(A_throat/pi);

Me = 0.12;
A = (k+1)/(2*(k-1));
B= k/(k-1);
C = 1/(k-1);
D = k-1;
E = k+1;
Pb = 2e6;
P_0 = 2.5e6;
L=100;
r=0;

delta_M = 0.1; %Increment between each mach number
M1_guess = 1+1e-4; %Initial guess for the subsonic mach number, must be less than one to ease convergence
iter_sub = 0;
iter_p=0;
error = 1e-6;
error1=6000;

x =1; 
while error1>1000
    
 for z=1:1:100
 r_position = sqrt((r_throat^2)*(1 + (2.5*((x/L)^2)))); %Radius at assumed shock location
 A_positon = pi*(r_position^2); %Area at assumed shock location
 
 shock_area = A_positon/A_throat; %Area ratio at the assumed shock location
 mach_shock_eqn = @(Ms,shock_area) ((1/Ms)*((2+(D*Ms^2))/E)^A) - shock_area; %Mach-Area equation

 dx=0.1;

    
    for i=1:1:100 %Number of iterations that will be done to reach the true value, 100 is the max number (abused)
        for j=1:1:100 %number of iterations 
        
        M_1= mach_shock_eqn(M1_guess,shock_area); %Mach number at initial guess
        M_2= mach_shock_eqn(M1_guess+delta_M,shock_area); %Mach number at next value
        
            if (M_1*M_2 >0)
                 M1_guess = M1_guess + delta_M; %New guess
            end
        
       if (abs(M_1-M_2) <=error)
            iter_sub =i;
       end
            
        end
     end

M_shock1 = M1_guess; %Mach number before the shock
M_shock2 = sqrt((M_shock1^2 + 2*C)/(2*B*M_shock1^2 -1)); %Mach number after the shock
  
P1 = P_0/((1+(0.5*D*(M_shock1^2)))^B); %Pressure before the shock
P2 = P1*(M_shock1/M_shock2)*((2+(D*(M_shock1^2)))/(2+(D*(M_shock2^2))))^0.5; %Pressure after the shock
     
P_02 = P2 *(1+0.5*D*(M_shock2^2))^B;
     
Pb_calc = P_02 / ((1+(0.5*D*(Me^2)))^B);

if (Pb_calc<Pb)
   x=x+dx;
else if (Pb_calc > Pb)
   x=x-dx;
else 
     x = x;
     break
     end
    
end
error1 = abs(Pb-Pb_calc)
 end
 end

y=x

Answer 1

[Cris LaPierre]

You appear to have one too many ends in your code. That's not going to fix your infinite loop, but it needs to be fixed, too.

Ultimately, your value for error1 does not change significantly. Perhaps check your equations, as well as the logic you use.