MATLAB: Repeat the iteration with an error using try/catch

catcherrorfor loopiterationnested looptry

I wrote a nested for loop to exexcute a huge number of iterations. However, sometimes an error stops the program. I want to repeat the iEv'th iteration in case an error occurs and then continue to next iteration. Please see below the code and let me know if it should be modified.

for iTcm=1:nTcm  
    for iScen=1:nScen
        for iEv=1:nEv
            try
              MyProgramHere
            catch ME
                disp(ME);
                fprintf('Retrying the program...\n');
            end
        end
    end
end

Best Answer

Maybe this construct does what you want

            while( true )
                try
                  MyProgramHere
                  break
                catch ME
                    disp(ME);
                    fprintf('Retrying the program...\n');
                end
            end

Related Solutions

MATLAB: How to force the next loop iteration if error occurs within the loop

The end is not the correct method to jump to the next iteration. Actually the continue command would solve this, but in your case no command is enough already:

for i=1:100
  try
    webread('www.something that could or could not generate an error.com')
  catch 
    % Nothing to do
  end
end

When you read this code in some years, the empty catch branch might look confusing like you've forgotten to program this part. So insert a meaningful comment why this is empty.

In most cases it is useful to display a comment when a try fails, or at least store a message in a protocol or something like this. If e.g. all iterations fail, the code will not perform anything and the user might get doubts about what's going on. In addition there could be a programming error or the inputs of webread might be changed in a future version of Matlab. Then try catch will hide the error message an the user has no chance to detect this. Therefore it is a fair strategy to treat the catch branch as obligatory:

for i=1:100
  try
    webread('www.something that could or could not generate an error.com')
  catch ME
    fprintf('WEBREAD without success: %s\n', ME.message);
  end
end

EDITED: The command "continue" will jump back to the surrounding for loop without processing the rest of the loop body:

for i=1:100
  try
    webread('www.something that could or could not generate an error.com')
  catch ME
    fprintf('WEBREAD without success: %s\n', ME.message);
    continue;  % Jump to next iteration of: for i
  end
  fprintf("WEBREAD worked successfully\n");
end

Now the success message will not appear in a case of an error. When there is no code behind the try-catch block, the continue has no effect, because there are no commands to be skipped.

Use continue carefully. In a bigger code this command can increase or reduce the readability. It might be "nicer" to move the success message insider the try branch. However, a descriptive comment is the best idea to state the purpose of continue clearly.

MATLAB: How to add/append column in an array in a for loop

Does this do what you want:

n_EVs = [2 3];
n_AGs = length(n_EVs)
Batt = [];
for k = 1 : n_AGs
    Batt = [Batt, 25 * ones(1, n_EVs(k))]
end

Output:

n_AGs =

Batt =

25 25

Batt =

25 25 25 25 25

And for n_EVs = [2, 3, 5] it gives:

Batt =

25 25

Batt =

25 25 25 25 25

Batt =

25 25 25 25 25 25 25 25 25 25

Best Answer

Related Solutions

MATLAB: How to force the next loop iteration if error occurs within the loop

MATLAB: How to add/append column in an array in a for loop

Related Question