How to use loop in Anonymous functions?

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Xiaohan Du
Xiaohan Du 2016-12-15
评论： Xiaohan Du 2016-12-15
Hi all,
I have a 2 by 2 cell 'dblk' like this:
dblk =
[4x4 double] [4x4 double]
[4x4 double] [4x4 double]
which contains 4 by 4 matrix in each cell block. Now I'd like to apply the same function on each block. The function sums all elements on all diagonal line, not just the main diagonal. I wrote the function as an Anonymous function:
diagsum = @(x) [sum(diag(x, -3)) sum(diag(x, -2)) sum(diag(x, -1)) ...
sum(diag(x, 0)) sum(diag(x, 1)) sum(diag(x, 2)) sum(diag(x, 3))];
Then I'm able to apply cellfun on dblk to get the summation result:
dblksum = cellfun(diagsum, dblk, 'UniformOutput', false);
The problem is in the Anonymous function 'diagsum', the sum(diag(x, n)), n starts from -3 to 3 cause the input is a 4 by 4 matrix, how can I make it apply to any matrix size?
Many thanks!

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采纳的回答

José-Luis
José-Luis 2016-12-15
编辑：José-Luis 2016-12-15
No need for a loop. You could define diagsum as follows, which should work for any square array:
n = 5;
values = rand(n);
diagsum = @(x) accumarray(reshape(bsxfun(@plus,(n:-1:1)',0:n-1),[],1),x(:))';
diagsum(values)

更多回答（1 个）

Adam
Adam 2016-12-15
I would probably just use a regular function in a file and create a handle to that. There is a limit to what you can do in an anonymous function. Maybe there is a way, including size(x,1) to get the size of your matrix, but it isn't easy to add extra calls to sum(diag(...)) in response to that.
You could create the function as a string and use str2fun possibly, but I would not recommend doing that when you could just create a regular function that is easily readable, understandable and debugable.

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