dolfin team mailing list archive

[Kent-Andre Mardal <kent-and@xxxxxxxxx>]

tor, 10.04.2008 kl. 12.48 +0100, skrev Garth N. Wells:
> 
> Kent-Andre Mardal wrote:
> > The new functions are the functions that have been added to
> > GenericVector, right ? 
> > 
> > I guess you refer e.g. to the fact that axpy have been re-implemented in
> > terms of a for loop instead of using the template expression y += a*x ?
> 
> Yes.
> 
> > The reason for this re-implementation is the operators implmented in
> > GenericVector. These operators mess up the operators previously
> > implemented by ublas_vector. 
> > 
> > What is the performance penalty ? 
> > 
> 
> uBLAS is better at performing various operations than we are. The 
> current implementation involves element access and the extra function 
> calls do have an impact for the size matrices we work with. We did 
> extensive testing some time ago, and the general conclusion was that 
> direct access to uBLAS functions is important for smallish vectors.
> 
> An unattractive feature of uBlasVector is that we have a mix-mash of 
> functionality from the uBlasVector interface and the ublas_vector 
> interface (including member functions with the same name). Should 
> uBlasVector simply own a ublas_vector and uBlasVector can return the 
> pointer to the ublas_object is a user needs it? This would mirror the 
> PETScVector design. Then we would know for sure where functions are 
> coming from.
> 
> > Does it help to change: 
> > 
> >   class uBlasVector : public GenericVector,
> >                       public Variable,
> >                       public ublas_vector
> > 
> > 
> > to 
> > 
> >   class uBlasVector : public ublas_vector,
> >                       public Variable,
> >                       public GenericVector
> > 
> > 
> > ?
> > 
> 
> I don't think so because uBlasVector re-implements some uBLAS 
> functionality (+=, -=, etc). I can't figure out how to wrap these 
> operators from uBLAS because they are very complicated.
> 
> Garth
> 

What I thought, but I have checked is that with the different sequence
of inheritance, the operators might not be re-implemented because the
operators from ublas would be used and not the operators of
GenericVector. But I have not checked and I have to go now. 


Kent