# bug #60515: trace documentation

 Submitter: None Submitted: Tue 04 May 2021 08:39:44 AM UTC Category: Octave Function Severity: 3 - Normal Priority: 5 - Normal Item Group: Documentation Status: Invalid Assigned to: None Originator Name: Originator Email: -email is unavailable- Open/Closed:  * Closed Release:  * 6.2.0 Operating System:  * Any
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## Discussion

Mon 30 Aug 2021 08:42:48 AM UTC, comment #3:

Kai Torben Ohlhus <siko1056>
Fri 20 Aug 2021 06:39:47 PM UTC, comment #2:

Is there anything to fix here?

John W. Eaton <jwe>
Tue 04 May 2021 09:27:16 PM UTC, comment #1:

It's generally understood from linear algebra that trace() applies to 2-D matrices.  Matlab also doesn't bother to document that N-dimensional arrays are excluded.

If you need a trace of a 2-D projection then you will need to use a for loop as you asked.  For example,

A = rand (3,3,3);
T = zeros (3,1);
for i = 1:3
T(i) = trace (A(:,:,i));
endfor

Rik <rik5>
Tue 04 May 2021 08:39:44 AM UTC, original submission:

A=rand(3,3,3);
x=trace(A)
error: trace: only valid on 2-D objects
error: called from
trace at line 37 column 5

Expected x to consist of 3 values.

## -*- texinfo -*-
## @deftypefn {} {} trace (@var{A})
## Compute the trace of @var{A}, the sum of the elements along the main
## diagonal.
##
## The implementation is straightforward: @code{sum (diag (@var{A}))}.
## @seealso{eig}
## @end deftypefn

The error is more clear.

---------------------------

Having many DCM and doing the trace.
Does this need to done in a loop?

Anonymous

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• -email is unavailable- added by siko1056 (Posted a comment)
• -email is unavailable- added by jwe (Posted a comment)
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