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

### Vaultec (view profile)

on 16 Jan 2015
Latest activity Commented on by Niels

### Niels (view profile)

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

### David Young (view profile)

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

### Vaultec (view profile)

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.

on 16 Jan 2015
Edited by Niels

### Niels (view profile)

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

### Vaultec (view profile)

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

### Niels (view profile)

on 20 Jan 2015
Check the edit I did just 1 minute after you replied again. :)