From help-octave-request  Thu May 27 14:12:23 1993
Subject: Re: sum(null matrix) becomes null matrix not zero 
From: John Eaton <jwe>
To: hasimoto at coral dot system dot nitech dot ac dot jp
Cc: twang at meishan dot animal dot uiuc dot edu, help-octave
Date: Thu, 27 May 93 14:12:19 EDT

: If I execute 
: >>a=[]
: >>b=sum(a)
: The result becomes b=[].
: Is this specification of octave?

It seems to me that any operation on an empty matrix should either
give you an error, or it should return an empty matrix.  You can
choose which you prefer by setting the value of the built-in variable
`propagate_empty_matrices' to either "true", "false", or "warn".

I suppose that a case could be made for treating the summation and
product functions as special cases (product should return 1?), but I
think it is probably better to try to avoid doing operations on empty
matrices.

: I expected b became zero like MATLAB.

I didn't know that Matlab returned 0.  Are you sure that's not a bug
in Matlab?

Are there very many places where this is really useful?

--
John W. Eaton      | The exam demonstrates a comminuted, slightly overlapping
jwe at che dot utexas dot edu|  | angulated fracture of the midfifth metatarsal.