Thread Subject:

given matrix, sum of diagonal elements

that, given a square matrix, returns the sum of the diagonal elements.

On Mar 8, 6:01 pm, "Enosh Bale" <fergysonnai...@gmail.com> wrote:
> that, given a square matrix, returns the sum of the diagonal elements.

doc sum
doc diag


Ex:
>> A = magic(5)
A =
    17 24 1 8 15
    23 5 7 14 16
     4 6 13 20 22
    10 12 19 21 3
    11 18 25 2 9
>> diag(A)
ans =
    17
     5
    13
    21
     9
>> sum(diag(A))
ans =
    65

-Nathan

Enosh Bale wrote:
> that, given a square matrix, returns the sum of the diagonal elements.

Create a new matrix B, which is the same size as the original matrix, A,
but only has the diagonal elements of A. Calculate the determinant of B.
The determinant will be the product of the eigenvalues, so factor the
determinant to get the eigenvalues. The sum of the eigenvalues of a
diagonal matrix is equal to the sum of the diagonal elements of the
matrix, so sum the factors you found to get the desired result.

Just another method, using linear indexing.

% Given A is nxn
n = 5;
A = magic(n);

% Linearly address the same elements as the DIAG function.
sum(A(1:n+1:n^2))

"Enosh Bale" <fergysonnaiyep@gmail.com> wrote in message <hn4a5i$j1p$1@fred.mathworks.com>...
> that, given a square matrix, returns the sum of the diagonal elements.

There's a special matlab function to do just that operation on a square matrix. Remarkably enough, it is called "trace".

Roger Stafford

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message
> There's a special matlab function to do just that operation on a square matrix. Remarkably enough, it is called "trace".
>
> Roger Stafford

D'oh. I am not sure I've ever even seen the TRACE function!
I do note that it is an M-File which uses:

t = sum(diag(a));

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message

Hi Roger,

It's good to see you again, after such a long break!
Did, by any chance, your email address change?

Jos

http://www.mathworks.com/matlabcentral/fileexchange/authors/10584

"Enosh Bale" <fergysonnaiyep@gmail.com> wrote in message <hn4a5i$j1p$1@fred.mathworks.com>...
> that, given a square matrix, returns the sum of the diagonal elements.

without using sum, diag(onal), or even TRACE :

ones(1,min(size(A))) * A(eye(size(A))==1)

Jos

"Jos (10584) " <#10584@fileexchange.com> wrote in message <hn5giv$89f$1@fred.mathworks.com>...
> "Enosh Bale" <fergysonnaiyep@gmail.com> wrote in message <hn4a5i$j1p$1@fred.mathworks.com>...
> > that, given a square matrix, returns the sum of the diagonal elements.
>
> without using sum, diag(onal), or even TRACE :
>
> ones(1,min(size(A))) * A(eye(size(A))==1)
>
> Jos

I like:

>> sum(A(1:size(A)+1:numel(A)))

Or without sum version:

>> A(1:size(A)+1:numel(A))*ones(length(A),1)