Is z an object here? How to interpret the code?

data = rand(4,4);
means = zeros(1,4);
parfor I = 1:4
    % The below usage of structures 
    % is flagged by Code Analyzer
    z.mean = mean(data(:,I));
    means(I) = z.mean;
end
disp(means)

Hi all, I found the above code was used to demonstrate incorrect use of parfor construct with MATLAB which can flag compiler errors.

On executing as expected with the code I encountered the an error stating The variable z in a parfor cannot be classified. See Parallel for Loops in MATLAB, "Overview".

what I fail to understand is 1) what is the datatype of z? is it a class an object ??? 2) but the code can be easily modified to handle the problem by replacing z.mean by z and the program runs perfectly. That makes me wonder why using z.mean is required??

Answer 1

[James Tursa]

z is a struct. It has a field named "mean".

[Aketh Thimmasandra-Maregowda]

but z is not been defined anywhere in the example?

It doesn't explain why a struct is need just to compute and store a mean of a value.

[James Tursa]

I don't know why a struct would be needed for that either. Just use z.

Where did the z.mean code come from in the first place? Did you inherit this code from someone or download it from somewhere? Does it complain if you do a direct assignment:

    means(I) = mean(data(:,I));

Is this just an exercise in finding out why parfor doesn't like the struct? (Seems counterproductive to use it for mean calculations)