finding neighbor value

Hi,

suppose I have a large matrix A of size 200X200

I need to know the neighbor value and also the neighbor position of distance 3 of the position (50,50)

can it be done easily

A =

     1     2     3
     3     3     6
     4     6     8
     4     7     7

here (2,2) value is 3. its one distance neighbor is 1,2,3,3,6,4,6,8 and position is (1,1),(1,2),(1,3),(2,1),(2,3), (3,1),(3,2),(3,3)

Answer 1

[Andrei Bobrov]

variant

A = randi(170,200);
sz = size(A);
center = [50 50];
N = 3;

Outnum = A(max(abs(repmat(1:sz(2),size(A,1),1) - center(1)) ,...
                 abs(repmat((1:sz(1))',1,size(A,2)) - center(2))) == fix(N/2));

more with bwdist from Image Processing Toolbox

A = randi(170,200);
sz = size(A);
center = [50 50];
N = 3;
AA = zeros(sz);
AA(center(1),center(2)) = 1;
Outnum = A(bwdist(AA,'chessboard')==fix(N/2));

Hi Oleg! Variant for N > 3

A = randi(170,17,13);
sz = size(A);
center = [8 7];
N = 5;

ons = ones(N);
ons(2:end-1,2:end-1) = 0;
ij = bsxfun(@plus, center.'-fix(N/2),0:N-1);
Outnum = A(ij(1,:),ij(2,:)).*ons;
Outnum = Outnum(Outnum>0);

[Oleg Komarov]

Too complicated IMHO.

[Sean de Wolski]

I'd roll with bwdist or A(imdilate(A == 3,ones(3)))

Answer 2

[Oleg Komarov]

EDITED

To make it flexible n = distance from center

A = randi(170,17,13);

center = [8 7];
n      = 2;

% Boundary check 
if all(pos - n) && all(pos + n <= size(A))
   B = A(center(1)-2:center(1)+2, center(2)-n:center(2)+n).';
   B = B([1:2*n*(n+1) 2*(n^2 + n + 1):end]);
end