How to calculate diagonal for NxN matrix ?

Hi

I'm trying to calculate the sum diagonal from a square matrix (size NxN). For example: A = [1 2 3 4; 5 6 7 8; 9 0 1 2; 3 4 5 6]; %square matrix Then if you would rotate the matrix by 45 degrees and take sum of the rotated martix. Like: imrotate(A,45)

What I'm trying to do is to find the diagonal sum of A. Therefore I want to construct a vector of size 1x(N+2) or for this A = [1 2 3 4; 5 6 7 8; 9 0 1 2; 3 4 5 6] it would be an vector of size 1x6.

Could you please help me? :)

[Azzi Abdelmalek]

what do you mean rotate 45°

[Lily]

Like imrotate(A,45)

[Jan]

Do you mean 90 deg instead of 45 deg?

[Honglei Chen]

I don't quite get it. Are you saying you want the sum along each diagonal? But if so, why is the resulting vector 1x(N+2)? Shouldn't it be 1x(2*N-1)? Could you post the desired answer for your sample matrix?

Answer 1

[Thomas]

YOu could use

 sum(diag(A))

this is essentially

 trace(A)

What does rotation by 45 mean

[Lily]

Like if I would imrotate(A,45)

[Thomas]

IF you use imrotate(A,45) you get a 9x9 matrix and not the 4x4 matrix you started with..

Answer 2

[Wayne King]

Just use trace()

trace(A)

[Lily]

Thx for the answer, but f I use trace(A) I only get the diagonal of the matrix A.

[Wayne King]

It's easy to say in general what an NxN matrix looks like for a multiple of 90 degrees, but what does it look like for 45? For N>3, I'm not sure what that looks like without padding the matrix with zeros like imrotate