## Conway's Game of Life implementation

Asked by Limbert Palomino

### Limbert Palomino (view profile)

on 14 May 2019
Latest activity Commented on by Geoff Hayes

### Geoff Hayes (view profile)

on 19 May 2019
Accepted Answer by Geoff Hayes

### Geoff Hayes (view profile)

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?

### Geoff Hayes (view profile)

Answer by Geoff Hayes

### Geoff Hayes (view profile)

on 15 May 2019
Edited by Geoff Hayes

### Geoff Hayes (view profile)

on 15 May 2019

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

### Limbert Palomino (view profile)

on 16 May 2019
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

### Geoff Hayes (view profile)

on 19 May 2019
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.