Help with while loop

I can't do this while loop properly, someone help me please?

[Rik]

Why did you delete your previous question? It is the same as this one.

[Hdez]

Thank you for your help

Answer 1

[Walter Roberson]

dt = input('Enter the desired time step: ');
while dt >= h^2 / (4*alpha)
    fprintf('solution is unstable\nPlease enter a value smaller than %g\n', h^2/(4*alpha));
    dt = input('Enter the desired time step: ');
end

Answer 2

[VBBV]

%f true
  dt = input('Enter the desired time step: ');
while dt <= h^2 / (4*alpha)
disp('The solution is stable')
if dt >= h^2 / (4*alpha)
  fprintf('solution is unstable\nPlease enter a value smaller than %g\n', h^2/(4*alpha));
  dt = input('Enter the desired time step: ');
end
end

You have missing end for if condition

[VBBV]

you can as well follow Walters solution. Its fine as it compares the instability condition in while loop itself. If you don't see the message , Enter the desired time step again then it implies solution is automatically stable.