code with while loop that start running but doesn't end
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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
回答(2 个)
Image Analyst
2023-1-20
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)
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