MATLAB: Indexing must appear last in an index espression

Xsum =A(1)(:,3); error is at this point for k = 2:299 Xsum=Xsum+A(k)(:,3); end

Best Answer

A(k) is the k.th element of the array A. Then indexing another time by "(:,3)" is not valid Matlab syntax. We cannot guess the purpose of this code, so please explain the class and dimensions of A and what you want to achieve.
[EDITED, after you provided the code]
I guess that:
Xsum = A(1)(:,3)
should be
Xsum =A{1}(:,3)
and the same for "Xsum=Xsum+A(k)(:,3)".
Compare it with the lines:
Ysum = A{1}(:,4); for m = 2:299 Ysum=Ysum+A{m}(:,4); end
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