matrix neighbours chaning with iterations

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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"?

Accepted Answer

Matt J
Matt J on 4 Nov 2013
[M,N]=size(A);
center=size(A)/2+.5;
[I,J]=ndgrid((1:M)-center(1), (1:N)-center(2));
A(:) = 20-5*round(max(abs(I),abs(J)))
  2 Comments
Jakub
Jakub on 4 Nov 2013
But what if i want to calculate the value of the "edge" by some formula? I need to adress the points..
Jakub
Jakub on 4 Nov 2013
And i want to have there any random numbers not just 20,15,10,... sorry

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