Counting the number of elements surrounding another element.

Hello,

I've created a matrix and have I randomly set one of these matrix elements equal to 1. Now I want to count how many elements are neighbouring it, I am taking into account diagonal neighbours too i.e. a fully surrounded element will have 8 neighbours etc.

Many thanks,

Phill

[Adam]

Just determine if it is on an edge (5 neighbours) or a corner (3 neighbours) and if not then as you say, it has 8 neighbours. No need to count them.

[Phillip Smith]

That works but I want to count the number of 0's around the element (since it's a matrix consisting of only 1's and 0's) and then change one of those 0's into a 1!

Answer 1

[Turlough Hughes]

If your matrix is called A. You could find the number of 0's surrounding an element at A(m,n) as follows:

D=padarray(A,[1 1],1,'both');
numberzeros=nnz(~D(m:m+2,n:n+2));

[Phillip Smith]

This helped and made me understand my greater goal. Thank you!

Answer 2

[Andrei Bobrov]

Let x - your array with ones and zeros:

x = double(rand(10) > .45);

out = conv2(double(~x),[1,1,1;1,0,1;1,1,1],'same');

[Phillip Smith]

could you explain to me what the 2nd line of your code is doing please?

[Andrei Bobrov]

Please read about conv2.