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Answer 1

+8 A:

Oops, it looks like someone is doing a homework assignment. Game of life maybe?

There are many ways to do such a test. But learn to do it in a vectorized form. This involves understanding how matlab does indexing, and how the elements of a 2-d array are stored in memory. That will take some time to explain in detail, more than I want to do at this exact moment. I would definitely recommend you learn it though.

Until then, I'll just suggest that if you really are doing the game of life, then the best trick is to use conv2. Thus,

A =[0     0     0     1     1     1     1     0
    0     1     1     1     1     1     1     0
    0     1     0     1     1     1     1     0
    0     1     1     1     1     1     0     0
    0     0     0     0     1     1     1     1
    1     1     1     1     1     1     1     1];

B = conv2(A,[1 1 1;1 0 1;1 1 1],'same')
B =
    1     2     4     4     5     5     3     2
    2     2     5     6     8     8     5     3
    3     4     8     7     8     7     4     2
    2     2     4     5     7     7     6     3
    3     5     6     7     7     7     6     3
    1     2     2     3     4     5     5     3

woodchips 2010-02-13 13:14:37

Wow, I wish I had known about conv2 back in the days when I was doing finite difference methods.

celion 2010-02-13 13:43:49

+1 - I think any other solution would be too convoluted. `conv2` is definitely the most elegant solution to the problem.

Jacob 2010-02-13 15:28:36

Was that pun intentional? :)

celion 2010-02-13 15:36:10

@Jacob: I agree. But just to answer the OP's question, maybe you should add `B==8` to detect elements whose 8-neighbors are all equal to 1. You can of course change the mask to check only for the immediate 4-neighbors (no diagonals)

Amro 2010-02-13 16:24:52

Also if you want to handle edges correctly, you might want to use the border replication options of the imfilter function, something like: `B = imfilter(A,[1 1 1;1 0 1; 1 1 1],'replicate','same','conv')==8`

Amro 2010-02-13 16:40:10

@celion: Yes, pun intended :)@Amro: That's an improvement, no doubt

Jacob 2010-02-14 00:34:39

Answer 2

+5 A:

Loren has recently posted about this very issue: http://blogs.mathworks.com/loren/2010/01/19/mathematical-recreations-tweetable-game-of-life/ - lots of interesting things can be learned by studying the code in that post and its comments

Yair Altman 2010-02-13 18:06:23

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Comparing adjacent elements in MATLAB

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