Conway's Game of Life implementation

Hello,

I am having trouble implementing my code for Conway's Game of Life. I know that the cases for killing cells are accurate and run well but for some reason the "birthing" cases don't seem to work. I am pretty sure my code covers all the cases so I don't know why my system just dies down eventually from the lack of new cells coming to life. Here is my code:

function GameOfLife(A)
B = conv2(full(A > 0),[0,0,0;0,1,0;0,0,0],'same');
while true
imshow(B);
drawnow;
	for i=2:size(B,1)-1
    	    for j=2:size(B,2)-1
        	C = B(i-1:i+1,j-1:j+1); % 3x3 Matrix with i,j point @ center
        	if B(i,j) == 1 % Cell is currently alive
            	    if (sum(sum(C)) < 3) || (sum(sum(C)) > 4)
                	B(i,j) = 0; % Dies
        	elseif B(i,j) == 0 % Cell is currently dead
            	    if sum(sum(C)) == 3
                	B(i,j) = 1; % Is born
            	end
            	end
            end
    	end
    end
end
end

Any ideas?

Answer 1

[Geoff Hayes]

Limbert - I think that part of the problem might be with how your if and elseif statements are not being properly "ended". For example, MATLAB may be interpreting this code

        	if B(i,j) == 1 % Cell is currently alive
            	    if (sum(sum(C)) < 3) || (sum(sum(C)) > 4)
                	B(i,j) = 0; % Dies
        	elseif B(i,j) == 0 % Cell is currently dead
            	    if sum(sum(C)) == 3
                	B(i,j) = 1; % Is born
            	end
              end
         end   

as

              if B(i,j) == 1 % Cell is currently alive
            	    if (sum(sum(C)) < 3) || (sum(sum(C)) > 4)
                	B(i,j) = 0; % Dies
        	    elseif B(i,j) == 0 % Cell is currently dead
            	        if sum(sum(C)) == 3
                	    B(i,j) = 1; % Is born
            	        end
            	    end
              end

Once you have finished with an if/elseif/else block, then you need to properly close it with an end. Your code might then become

              if B(i,j) == 1 % Cell is currently alive
            	    if (sum(sum(C)) < 3) || (sum(sum(C)) > 4)
                	B(i,j) = 0; % Dies
             	    end             % <-------------------------- this is important!!
        	elseif B(i,j) == 0 % Cell is currently dead
            	    if sum(sum(C)) == 3
                	B(i,j) = 1; % Is born
            	    end
             	end

Also, rather than executing the same calculation 2-3 times, just do it once

numberOfNeighbours = sum(sum(C));

and use this variable when comparing against three or four.

[Limbert Palomino]

Thank you!

I got it working almost right after I posted this but I found that the bug I had was because the for loops wasn't iterating through all my statements, so I wrote a second one. Would ending loops like this, and creating a variable to avoid repeating the operation many times increase the efficiency of the function overall?

[Geoff Hayes]

I would have to see more of your code but adding a variable "to avoid repeating the operation many times" may not be the best way to go.