In your case, it will go away if you modify the loop as
parfor i=1:iLen
matrix(i,:)=jVal;
end
It's not an error, but rather a warning that you might not have efficient code. MATLAB sees that you are indexing a matrix variable inside the loop using another variable j. This usually means the matrix variable is a large array. If it were a small array, you would usually just index it with known, fixed constants, like jVal(1). If it is a large array, you usually want to find a way to have parfor send to the worker only a slice of the array that the worker will use, instead of broadcasting the whole array to every worker.
