From help-octave-request at bevo dot che dot wisc dot edu Thu Dec 19 18:56:54 2002
Subject: Re: A bit puzzled...
From: Al Niessner <Al dot Niessner at jpl dot nasa dot gov>
To: Paul Kienzle <pkienzle at users dot sourceforge dot net>
Cc: Octave Help <help-octave at bevo dot che dot wisc dot edu>
Date: 19 Dec 2002 19:58:43 -0500


It all works now. Apparently 25 years away from Fortran made my code a
little error prone. I octave with ddd (gdb front end basically) and was
able to find the problem in no time. It was in my code -- obviously. 

Thank you for your help and patience. 

Al Niessner 

On Wed, 2002-12-18 at 23:55, Paul Kienzle wrote: 
> 
> ----- Original Message -----
> From: "Albert F. Niessner" <Al dot Niessner at jpl dot nasa dot gov>
> To: "Paul Kienzle" <pkienzle at users dot sourceforge dot net>
> Cc: "Octave Help" <help-octave at bevo dot che dot wisc dot edu>
> Sent: Wednesday, December 18, 2002 3:19 PM
> Subject: A bit puzzled...
> 
> 
> >
> > Thanks for your responses to my posts, but your replies have me a bit
> > puzzled.
> >
> > In one of them
> > (http://www.octave.org/mailing-lists/help-octave/2002/1164), you wrote:
> > "The data is not actually copied until you do A.fortran_vec() to access
> > the data for modification."
> >
> > However, in the other
> > (http://www.octave.org/mailing-lists/help-octave/2002/1163) you wrote:
> > "If the operation is not in place, or if you need a working vector,
> > allocate it beforehand:
> >
> >     octave_value_list retval;
> >     const Matrix A(args(0).matrix_value());
> >     const Matrix B(args(1).matrix_value());
> >     Matrix C(A.rows(),B.columns());
> >     F77_FUNC(f,F)(A.data(),B.data(),C.fortran_vec());
> >     retval(0) = C;
> >     return retval;"
> >
> > But, if the data is being copied at the C.fortran_vec() routine, then
> > retval(0) = C cannot possibly contain the answer.
> 
> I should have said that C.fortran_vec() checks the reference count for the
> data in matrix C, and if it is greater than 1, allocates new data for C,
> copies the values from the old data to the new data and decrements the
> reference count in the old data.  C.fortran_vec() does not return a copy
> of the data --- it returns the real data but with the assurance that no
> other
> matrix is referencing it.  That way when you change the data directly, you
> can be sure that no matrices other than C are affected.
> 
> Does this help?
> 
> Paul Kienzle
> pkienzle at users dot sf dot net
> 
> 
> 
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Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
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