[Octave-bug-tracker] [bug #29942] concatenating with an empty scalar gives an error

[Ben Abbott]

Follow-up Comment #4, bug #29942 (project octave):

The Matlab code I found this in was written in 2002, and I'm running 2009b.
So this behavior appears to have been around a while.

Perhaps your recollection is with regards to cat()?

>> cat (1, zeros(1,0), 1)
??? Error using ==> cat
CAT arguments dimensions are not consistent.
 
>> cat (2, zeros(1,0), 1)

ans =

     1

>> cat (2, zeros(0,1), 1)
??? Error using ==> cat
CAT arguments dimensions are not consistent.
 
>> cat (1, zeros(0,1), 1)

ans =

     1

For cat(), Matlab and Octave behave the same way.

Mathwork's description for how "[...]" works is

"Vectors and matrices can be used inside [ ] brackets. [A B;C] is allowed if
the number of rows of A equals the number of rows of B and the number of
columns of A plus the number of columns of B equals the number of columns of
C. This rule generalizes in a hopefully obvious way to allow fairly
complicated constructions."
--
http://www.mathworks.com/access/helpdesk/help/techdoc/ref/specialcharacters.html

The way Matlab functions isn't consistent, but I hesitate to conclude this is
due to a bug, a feature, or intent.

The original context was I discovered this in was ...

a = []
do ...
  b = ...
  a = [a(n:end);b]
end

I don't expect the typical user would realize that "a" and "a(n:end)" will
have different shapes when "a" is empty. So Mathworks may have chosen this
approach as a path of least resistance.

In either event, I agree that the way Octave behaves is consistent and
technically proper. So, I have no problem leaving it as it is. However, I'm
not sure if this is a Matlab bug or incompatibility on the part of Octave.

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