MATLAB: MatLab code runs indefinitely since adding while loop

matlab crash

I had a code which ran but wasn't giving me the right output so I changed an if lop to use a while loop instead and now when I run the code it runs indefinitely and I'm not sure why or what I can do to fix it. Have tried closing & reopening, removing while loop and then running without, using a different computer but all to no avail! Any help greatly appreciated! Cheers P.s, have tried to use the {} brackets but not sure it's all coming out right :/
Code {
m=4000;                    %kg
g=9.81;                     
L=4;                        %m



r_min=1.2;                  %m
r_max=2.2;                  %m
r=linspace(1.2,2.2,37);              %m
theta_min=-20;              %degrees




theta_max=80;               %degrees
theta=linspace(-20,80,37);             %degrees
phi=linspace(0,180,37);                %degrees
gamma=phi+20;               %degrees
%-----------------------------------
      F_max=0;
for i=1:37
    c_2(i)=((r_max^2)-(r_min^2))./(cosd(gamma(i)+theta_min)-cosd(gamma(i)+theta_max));
    c_1(i)=(r_min^2)+c_2(i).*cosd(gamma(i)+theta_max);
    a(i)=real(0.5*(((c_1(i)+c_2(i)).^(1/2))+((c_1(i)-c_2(i)).^(1/2))));
    b(i)=real(c_2(i)/(2*a(i)));
    for j=1:37
        r(i,j)=sqrt((a(i)^2)+(b(i)^2)-(2*a(i)*b(i)*cosd(gamma(i)+theta(j))));
        F(i,j)=(r(i,j)*m*g*L*cosd(theta(j)))/(b(i)*a(i)*sind(gamma(i)+theta(j)));
        plot(theta,F(i,j));
    end
    while F(i,j)>F_max
        F_max_new=F(i,j);
    end
    F_max=F_max_new
  end
}

Best Answer

Cat - you should format your code so that it is readable. Just highlight the code portion and press the {} Code button.
It looks like your while loop is just the code
 while F(i,j)>F_max
    F_max_new=F(i,j);
 end
So if the condition F(i,j)>F_max is true, then the body of the loop is executed which just sets F_max_new to a new value, then the condition is checked again. But since nothing has changed with respect to either F_max or F(i,j), then the condition is once again satisfied/true, so we execute the body of the loop. This continues without change and so the code becomes "stuck" in this loop.
If you are just trying to find the maximum value of F, then you could do this after you have finished the for loops. Just do
 F_max = max(F(:));
and that will return the maximum value of F, and so you can avoid using the while loop.
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