# how do I select every single element of matrix except middle

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Vaultec on 16 Jan 2015
Commented: Niels on 20 Jan 2015
Say for example I have a 3 by 3 matrix
[1,2,3;4,5,6;7,8,9]
How do I select every element of the matrix except for the middle element?

David Young on 16 Jan 2015
What do you mean by "select"? In other words, what operation are you going to carry out on the non-central elements?
Vaultec on 16 Jan 2015
Well any operation really, For example if multiply by 2 -1. Basically I want to be able to alter every single element except the central element.

Niels on 16 Jan 2015
Edited: Niels on 16 Jan 2015
If I understand you correctly, you could do something like this:
A(A~=A(ceil(numel(A)/2)))
or
setdiff(A,A(ceil(numel(A)/2)))
Assuming you always have an odd number of elements these approaches should work.
Considering your edit, you could do it like this:
B = A([1:ceil(numel(A)/2)-1, ceil(numel(A)/2)+1:end]) * whatever;
Or, keeping it within A;
A([1:ceil(numel(A)/2)-1, ceil(numel(A)/2)+1:end]) = ...
A([1:ceil(numel(A)/2)-1, ceil(numel(A)/2)+1:end]) * whatever;

Vaultec on 16 Jan 2015
Sorry that wasnt what I was looking for. Is there anything similar to A(1:3,1:3) and someway to remove the middle element or set it to 0 as I simply want to do operations on the remaining 8 elements
Niels on 20 Jan 2015
Check the edit I did just 1 minute after you replied again. :)