From help-octave-request at bevo dot che dot wisc dot edu  Thu Nov  5 23:23:34 1998
Subject: Empty Matrix DLD question
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Andy+Alison Adler <adler at mondenet dot com>
Cc: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 5 Nov 1998 23:23:09 -0600 (CST)

On  5-Nov-1998, Andy+Alison Adler <adler at mondenet dot com> wrote:

| I'd like to return an empty matrix from
| an *oct file.
| 
| Initially I hoped that when cx==0
| 
|     X["ridx"]= ridxX.extract( 0, cx-1);
| 
| would return an empty matrix.
| No luck. x.ridx is a two element column vector.
| 
| Next, I tried
| 
|    if ( cx > 0 ) {
|       X["ridx"]= ridxX.extract( 0, cx-1);
|    } else {
|       ColumnVector nullvec(0);
|       X["ridx"]= nullvec;
|    }
| 
| But this segfaults octave.

Hmm.  I can't reproduce the problem given just this information.  Can
you please send a copmlete bug report to bug-octave that includes a
copmlete test case that demonstrates the bug?

| I couldn't find any examples of how to do this
| in the source.
| 
| Is there an approved way to create empty matrices?

Try

  X["ridx"] = Matrix ();

Thanks,

jwe