Difference between debug parfor loop and run it
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I have the following question: Whats the differnce between debugging a parfor loop and run it? In the matter that i stop executing the code before the parfor loop and then execute the hole parfoor loop with pressing F9.
Because, if i debug the parfor loop it can be execute without any error but if I run it normally the following error message appears:
"for the parfor-loop that is trying to execute on the worker could not be found."
Unrecognized function or variable 'A'.
Error using remoteParallelFunction (line 94)
Worker unable to find file.
Unrecognized function or variable 'A'."
Before the parfor-loop gets called other function gets called and the parfor-loop is also calling a other function. The called function makes some calculation and saving stuff to the file system, nothing else. So I am a bit confused, because variable 'A' is a variable that isn't changed and every iteration gets variable A.
Thanks for the help already!
Edric Ellis on 27 May 2022
Further to Walter's answer, parfor assumes that anything that is not statically provable to be a variable reference must be a function reference. In your case, I suspect you're using eval or load to generate the variables A etc. The parfor machinery is therefore unable to transfer A to the workers, and instead assumes A is the name of a function - which it then can't find. Here's a simple example which shows the problem:
function out = doStuff()
eval('A = 1;');
parfor i = 1
out(i) = A(i);
If this is indeed the problem, then the fix is simple: don't use load or eval - ensure the variables are defined in the text of the program normally.
More Answers (2)
Walter Roberson on 27 May 2022
parfor is not always able to automatically determine which functions will be called by workers, especially if eval() or run() is used or if you have calls to an optimization or ode* function that uses a quoted string for the function name instead of using a function handle.
In order to tell parfor where to find the files you may need to attach them to the pool.
Over the longer term, if you are using quoted strings for function names you should probably rewrite to use anonymous functions.