How to increase maximum number of iterations in a 'for' loop, when in the loop?

Question

Kaushal Sorte 2020-11-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/654608-how-to-increase-maximum-number-of-iterations-in-a-for-loop-when-in-the-loop

评论： Steven Lord 2020-11-20

A = [9 1 2 3; 1 7 2 3; 1 5 10 2; 1 2 3 9] 
B = [1;2;3;4]
n = size(B,1);
Tolerance = 10^-15;
x = zeros([n,1]);      %Initialization vector defaultly set as zero for ease of operation.
Norm_Values = [];      % Storing first norm values.
K = 10;
for k = 1:K
    T = x;             % Storing previous x vector
    for i = 1:n
        x(i) = (B(i) - A(i,[1:i-1 i+1:n])*x([1:i-1 i+1:n]))/A(i,i);
    end
if (norm((x-T),1) <  Tolerance)                                                  % Checking for convergence.
    fprintf('GaussSeidel has converged in %d iterations.\n',k)
    break
elseif (k == K)
    K = K + 10             %Extending for loop 
end
end

Could somebody please help me with this problem?

If the norm does not go below tolerance within K iterations, I want to increase the number of iterations. But it is not working. It is only going up to 10 iterations.

(Above is just parts of the whole code.)

I don't want to use 'while' here because I would then have to do the 1st iteration outside the loop.

Help will be appreiciated.

Thanks in anticipation.

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Answer 1

Alan Stevens 2020-11-20

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/654608-how-to-increase-maximum-number-of-iterations-in-a-for-loop-when-in-the-loop#answer_550948

在 MATLAB Online 中打开

Use a while loop instead

while (norm((x-T),1) >  Tolerance) 
    ...etc
end

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Rik 2020-11-20

It might be possible, but you should not do that. If you don't know the iterator values in advance, you should use a while loop.

You can also use the higher number of iterations and use break inside an if statement, but that will not work for your setup.

Steven Lord 2020-11-20

No. As soon as you enter the for loop, MATLAB calculates the values of the loop variable over which it iterates. You can (but shouldn't) change the loop variable inside the body, but any such changes will be overwritten with the next iterate at the start of the next execution of the body of the loop.

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