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How to Sum matrix diagonals

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Krish Desai
Krish Desai 2015-9-27
评论： Tia Miller 2018-10-15
If I have the following matrix
a = [1 2 3; 4 5 6; 7 8 10
a =
1 2 3
4 5 6
7 8 10
How do I sum the diagonal of 7,5,3? I know that to sum 1,5,10 I use
sum(diag(a))
But when I try
sum(diag(a,2))
The answer is 3. Is there a built in function that calculates the sum, or do I have to make a while loop?
  1 个评论
Tia Miller
Tia Miller 2018-10-15
sum(diag(a,2)) is summing the diagonal 2 away from the main diag, which has one entry, 3.
sum(diag(flip(a))) will sum 3, 5, 7, or the main diag after the matrix has been flipped

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2015-9-27
编辑：Andrei Bobrov 2015-9-27
sum(diag(a(:,end:-1:1)));
or summing all diagonals:
sum(spdiags(rot90(a)));

更多回答（2 个）

John D'Errico
John D'Errico 2015-9-27
sum(diag(flip(A)))
should work.
Ahmed Diaa
Ahmed Diaa 2018-5-5
x=sum(diag(E));% calculating the normal diagonal
y=sum(diag(flip(E)));% calculating the inverse diagonal
z=[];% subtracting the common element
s=y+x-z ;% the sum

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