code with while loop that start running but doesn't end

The code is designed to resolve (via a while loop) a least square adjustment problem, unknowns are a,b,c, observations y and constant x values such that : y(x) = a* exp(b*x) +c.

The code starts running but never ends, I don't know what to change..

Thank you in advance for your precious help.

% data: x and L are both 25x1  vector (scalars) 
data = importdata('exercise9task2.txt');
x= data(:,1);
L=data(:,2);

%break-off conditions
epsilon = 10^-6;
delta = 10^-8;
max_x_hat = 1;
check2=1;

%Number of iterations
iteration = 0;

syms a1 b1 c1
bx= a1* exp(x.*b1 ) +c1;



     while  check2 > delta && max_x_hat >  epsilon  
    
     %Observations as functions of the approximations for the unknowns
     L_0 = subs(bx,{a1,b1,c1},{X_0(1),X_0(2),X_0(3)});
     
     %Vector of reduced observations
     l = L-L_0;
    
     %Design matrix with the elements from the Jacobian matrix J
     
     A = jacobian(bx) ;
     A= subs(A,{a1,b1,c1},{X_0(1),X_0(2),X_0(3)});
    
     %Normal matrix
     N = A'*A ;
     
     %Vector of right hand side of normal equations
     n = A'*l;
    
     %Inversion of normal matrix / Cofactor matrix of the unknowns
%      Q_xx =inv(N) ;
    
     %Solution of the normal equations
     x_hat = inv(N) *n;
        
     %Update
     X_0 = x_hat + X_0;
    
    
    
     %Check 1
     max_x_hat = max(abs(x_hat));
     
     %Vector of residuals
     v = A*x_hat - l;
 
     %Vector of adjusted observations
     L_hat = L+v;
    
     %Objective function
%      vTPv = v'*v;
    
     %Functional relationships witho    ut the observations
     

     %Check 2
     Check2 = max(abs(L_hat - (subs(bx,{a1,b1,c1},{X_0(1),X_0(2),X_0(3)}))));
    
     %Update number of iterations
     iteration = iteration+1;
  
     end

[Les Beckham]

Matlab is case sensitive, so Check2 and check2 are not the same thing. You are never defining check2 so that portion of your while test will never be triggered. Try fixing that issue and see if it helps.

[Moufid Tarek]

Thank you for your help, it was something I didn't even notice, but the problem remains

[Moufid Tarek]

It seems like it is not able to compute the value of Check2, I tried running each line on its own, and the check2 line runs but doesn't end

Answer 1

[Image Analyst]

While loops should always have a failsafe so you don't get an infinite loop. Here is an example of how to put a failsafe in your loop:

% Demonstration of how to avoid an infinite loop by setting up a failsafe.
% Set up a failsafe
maxIterations = 100; % Way more than you think it would ever need.
loopCounter = 0;
% Now loop until we obtain the required condition: a random number equals exactly 0.5.
% If that never happens, the failsafe will kick us out of the loop so we do not get an infinite loop.
r = nan; % Initialize so we can enter the loop the first time.
while (r ~= 0.5) && loopCounter < maxIterations
    loopCounter = loopCounter + 1;
    fprintf('Iteration #%d.\n', loopCounter)
    r = rand; % This will never equal 0.500000000000000000000000000000 exactly
end
% Alert user if we exited normally, or if the failsafe kicked us out to avoid an infinite loop.
if loopCounter < maxIterations
    % Then the loop found the condition and exited early, which means normally.
    fprintf('Loop exited normally after %d iterations.\n', loopCounter);
else
    % Then the loop never found the condition and exited when the number of iterations
    % hit the maximum number of iterations allowed, which means abnormally.
    fprintf('Loop exited abnormally after iterating the maximimum number of iterations (%d) without obtaining the exit criteria.\n', maxIterations);
end
fprintf('All done after %d iterations.\n', loopCounter)

[Moufid Tarek]

Thank you, it is very good to know that, I will keep that in mind.

My code, on the otherhand, is not good enough to perfom more than one loop, if I stop the code from running and check the variable iteration, it is equal to 0

Answer 2

[Moufid Tarek]

Thank you all for your support. I found the solution, everywhere I used the equation "bx" I had to convert the output to "double"

For instance:

L_0 = subs(bx,{a1,b1,c1},{X_0(1),X_0(2),X_0(3)});
% should be 
L_0 = double(L_0); % before being used in other computations
% in order to make it work