From help-octave-request at bevo dot che dot wisc dot edu  Tue Feb 10 15:30:32 1998
Subject: Re: Empty matrix question
From: "Wonkoo Kim" <wkim+ at pitt dot edu>
To: "Andy Adler" <adlera at njc dot org>,         "Octave Users" <help-octave@bevo.che.wisc.edu>
Date: Tue, 10 Feb 98 16:20:25 -0500

> Date: Tue, 10 Feb 98 12:00:15 -0700
> From: "Andy Adler" <adlera at njc dot org>
> Subject: Empty matrix question
>
> I'm having a problem with empty matrices.
>
> There's probably an octave preference variable to do this
> but I couldn't find it. (So far 90% of my questions to
> help-octave have been answered by a preference variable)
>
> Anyway, here's the sample code
>
>   octave:54> vector=ones(1,5);
>   octave:55> numfix=0;
>   octave:56> vector(1:numfix)=zeros(numfix,1);
>   error: A([]) = X: X must also be an empty matrix
>   error: evaluating assignment expression near line 56, column 17
>
> "numfix" is not necessarily zero in the "real" code, but can
> be zero if there are no elements to "fix"

I don't see a statement in a octave's doc, but I would recommend you
to allocate memory (i.e. assign) without indexing.  So the above can 
be done as

octave:1>numfix = 5
numfix = 5
octave:2>vector = zeros (numfix, 1)
vector =

  0
  0
  0
  0
  0

octave:3>

> I realize that I could fix this code using something like
>
>   octave:56> vector(1:numfix)=zeros(numfix, (numfix>=1) );

This does not solve.

//--------------------------------------------------------------------
// Wonkoo Kim (wkim+ at pitt dot edu)