Skipping iteration on child throwing a warning

Question

Aboltabol 2023-9-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026854-skipping-iteration-on-child-throwing-a-warning

评论： Bruno Luong 2023-9-28

I have a script X that has:

for x = 1:5000
    output{x} = Script_Y(input(:,:,:,x));
end

Script_Y has a particular loop (among other code):

for alpha = 1:(size(input, 3)-1)
    output_preprocessed = Script_Z(input(:,:,alpha), input(:,:,alpha+1));
end
% Later, some more operations are committed on output_preprocessed to give
% the function output.

Script_Z has a loop (among other code):

% Some operations are committed on function inputs to get input_postprocessed_1 and input_postprocessed_2
for k = 1:200
    x = input_postprocessed_1/input_postprocessed_2
    % More steps to make x precise %
end
% Later, some more operations are committed on x to give
% the function output.

It might occur that for some k, input_postprocessed_1 is singular or near-singular and as soon as Matlab throws this warning, I want to skip the particular iteration in the master loop at my script X! For that x, output{x} shall return NULL or nothing - either sufices for me.

How to go about?

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Image Analyst 2023-9-28

What exactly is the warning? Please paste back here all the orange or red text that you see when it produces the warning.

Bruno Luong 2023-9-28

@Image Analyst OP wrote " input_postprocessed_1 is singular or near-singular "

Actually it input_postprocessed_2 at the right division and the warning is likely the infamous

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = XXXXXX.

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Answer 1

Bruno Luong 2023-9-28

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026854-skipping-iteration-on-child-throwing-a-warning#answer_1321064

编辑：Bruno Luong 2023-9-28

在 MATLAB Online 中打开

Modification of script_Z

for k = 1:200
    lastwarn('',''); % clean the warning state
    x = input_postprocessed_1/input_postprocessed_2;
    [~,warnid] = lastwarn;
    if strcmp(warnid, 'MATLAB:singularMatrix');
        x = []; % I assume this is output_preprocessed returned to script Y
        break
    end
    % More steps to make x precise %
end

script_Y

for alpha = 1:(size(input, 3)-1)
    output_preprocessed = Script_Z(input(:,:,alpha), input(:,:,alpha+1));
    if isempty(output_preprocessed)
        break
    end
end

script_X

for x = 1:5000
    output{x} = Script_Y(input(:,:,:,x));
    % output{x} is empty if the division fails ( input_postprocessed_2is
    % singular)
end

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Answer 2

Image Analyst 2023-9-28

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026854-skipping-iteration-on-child-throwing-a-warning#answer_1321054

在 MATLAB Online 中打开

You can use try catch:

for k = 1 : 200
    try
        % In the try block put the code that might throw an error.
    catch ME
        % If you get here an error occurred.
        continue; % To continue with next iteration, or use "break" to exit the loop.
    end
end