How to resolve indexing the sliced variable error in the case of for nested with parfor?

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Rahul Bhadani
Rahul Bhadani on 29 Apr 2021
Answered: Edric Ellis on 30 Apr 2021
I have following use case:
Nth = 102;
p = 0.0000001:0.1:0.99999;
NthArray = (Nth - 100 > 0)*Nth + (Nth - 100 <=0)*1:1:Nth+100;
III = zeros( length(p), length(NthArray));
parfor ip = 1:numel(p)
for inth = 1:numel(NthArray)
III(ip, inth) = g( p(ip), ntharray(inth));
end
end
However, upon running it I get following error:
Error: When indexing the sliced variable 'III', the range of the for-loop variable 'inth' must be a row vector of positive constant numbers or variables. For more information, see Parallel
for Loops in MATLAB, "Nested for-Loops with Sliced Variables".
How should I resolve this error?
Thanks.

Answers (1)

Edric Ellis
Edric Ellis on 30 Apr 2021
The problem here is that the inner loop bounds must be a constant - basically this means that you must compute it outside the parfor loop, like so:
Nth = 102;
p = 0.0000001:0.1:0.99999;
NthArray = (Nth - 100 > 0)*Nth + (Nth - 100 <=0)*1:1:Nth+100;
III = zeros( length(p), length(NthArray));
% Must calculate inner loop bounds outside the PARFOR loop:
n_Nth = numel(NthArray);
g = @plus; % Dummy definition of "g"
parfor ip = 1:numel(p)
for inth = 1:n_Nth
III(ip, inth) = g( p(ip), NthArray(inth));
end
end
disp('Success!')
Success!

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