MATLAB: How to adress neighbours in matrix

adressImage Processing Toolboxiterationmatrix

Imagine I have matrix A=ones(5). I want to change center of the matrix to 17, A(3,3)=17; In next iteration I want to change all points that are next to this 20 to 5. i will have:
1  1  1  1  1
1  5  5  5  1
1  5 17  5  1
1  5  5  5  1
1  1  1  1  1
In next step i want to change all ones to 10. And so on...
10 10 10 10  10
10  5  5  5  10
10  5 17  5  10
10  5  5  5  10
10 10 10 10  10
Any idea how to do this to large matrix? How to adress only the neighbours but not the points "inside"?

Best Answer

This works for any size matrix, large or not, as long as it's bigger than 5x5. Also you can't get a center element if there is an even number of rows or columns.
A = ones(9)
centerRow = ceil(size(A, 1)/2)
centerCol = ceil(size(A, 2)/2)
A(centerRow-2:centerRow+2, centerCol-2:centerCol+2) = 20;
A(centerRow-1:centerRow+1, centerCol-1:centerCol+1) = 10;
A(centerRow, centerCol) = 17
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