MATLAB: How to check adjacent matrix values for a value

matrix

function e=evosim()
board=(zeros(12,12));
pop=1;
charac=([1, 0]);
cloc=[];
for i=1:pop             %%Population generator%%
    popcount=1;
    a=randi([1,12]);
    b=randi([1,12]);
    if board(a,b)==0
        board(a,b)=charac(1);
        cloc=[b a popcount; cloc]
    end
end
for i=1:10              %%Food generator%%
    a=randi([1,12]);
    b=randi([1,12]);
    if board(a,b)==0
        board(a,b)=2;
    end
end
e=board;
for i=1:pop
    xcord=cloc(i,1);
    ycord=cloc(i,2);
    if board(xcord-1,ycord)==2
        
end
Here's my code so far: basically, I have a blank 12×12 matrix, and randomly place 1's and 2's. I want to check the 8 squares around the 1, and the x and y coordinates of any 1s are stored in cloc. After it checks, I want the 1 to 'jump' to the location of where the 2 was.
I think I could do it by checking for (xcord+-1, ycord+-1,) etc, and recording the coordinates of the matrix 1s. However, I was wondering if there was a more efficient way of doing this.
I am new to matlab as well, so any suggestions are more than welcome in improving my code! Thanks!

Best Answer

I don't understand the rules of evolution of the board that you described. However, an efficient way to gather all the 8-neighbor groups for subsequent analysis is as follows. Here, I've used a 4x4 board size for illustration,
n=4; %board size
[I,J,dI,dJ]=ndgrid(1:n,1:n,-1:1,-1:1);
I=reshape(I+dI,[],9); clear dI
J=reshape(J+dJ,[],9); clear dJ
valid=(I>=1 & I<=n) &  (J>=1 & J<=n);
I(~valid)=nan;
J(~valid)=nan;
lookup=sub2ind([n,n],I,J);
lookup(~valid)=1;
lookup(:,5)=[];
valid(:,5)=[];
mask=double(valid); mask(~valid)=nan;
The key results of this are lookup and mask. You would compute them only once and pass them to your function for repeated use. You use them as follows, to form a matrix whose rows are the neighbors of successive locations on the board. The NaNs indicate nieghbors outside the boundaries of the board.
board=rand(n),
board = 4×4
    0.9145    0.9106    0.0653    0.7765
    0.3478    0.6923    0.7918    0.1343
    0.9213    0.8086    0.7676    0.8892
    0.1573    0.2661    0.0432    0.7342

neighbors = board(lookup).*mask
neighbors = 16×8
       NaN       NaN       NaN       NaN    0.3478       NaN    0.9106    0.6923
       NaN       NaN       NaN    0.9145    0.9213    0.9106    0.6923    0.8086
       NaN       NaN       NaN    0.3478    0.1573    0.6923    0.8086    0.2661
       NaN       NaN       NaN    0.9213       NaN    0.8086    0.2661       NaN
       NaN    0.9145    0.3478       NaN    0.6923       NaN    0.0653    0.7918
    0.9145    0.3478    0.9213    0.9106    0.8086    0.0653    0.7918    0.7676
    0.3478    0.9213    0.1573    0.6923    0.2661    0.7918    0.7676    0.0432
    0.9213    0.1573       NaN    0.8086       NaN    0.7676    0.0432       NaN
       NaN    0.9106    0.6923       NaN    0.7918       NaN    0.7765    0.1343
    0.9106    0.6923    0.8086    0.0653    0.7676    0.7765    0.1343    0.8892
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