[Trilinos-Users] Trilinos-Users Digest, Vol 60, Issue 1

[Bartlett, Roscoe A]

Chris,

Expression templates generate new code right when you write:

   y = alpha * x1 + beta * x2;

and then gets optimized away by the compiler to a flat fused loop.

See:

   http://en.wikipedia.org/wiki/Expression_templates

which also references the original ET article.

How would this code get this ET compiled by CUDA and run on the GPU?

- Ross


> -----Original Message-----
> From: Baker, Christopher G. [mailto:bakercg at ornl.gov]
> Sent: Monday, August 02, 2010 12:55 PM
> To: Bartlett, Roscoe A; Hoemmen, Mark; trilinos-
> users at software.sandia.gov
> Subject: Re: [Trilinos-Users] Trilinos-Users Digest, Vol 60, Issue 1
> 
> I'm not sure why "expression templates will not work when the data is
> on a GPU". Can you elaborate?
> 
> Chris
> 
> 
> On 8/2/10 2:51 PM, "Bartlett, Roscoe A" <rabartl at sandia.gov> wrote:
> 
> Expression templates will not work when the data is on a GPU.
> 
> My stop-gap measure for linear algebra operations is given here:
> 
> 
> http://trilinos.sandia.gov/packages/docs/dev/packages/thyra/doc/html/Li
> nearAlgebraFunctionConvention.pdf
> 
> with examples at:
> 
> 
> http://trilinos.sandia.gov/packages/docs/dev/packages/thyra/doc/html/cl
> assThyra_1_1VectorBase.html
> 
> Therefore, for:
> 
>    y = alpha * x1 + beta * x2
> 
> you would have:
> 
>   V_StVpStV( y, alpha, x1, beta, x2 );
> 
> This is not the most beautiful thing you have ever seen but at least
> you can go back and forth between the linear algebra notation and the
> function declaration and call sequence.  You can also make this run
> very fast without fancy expression templates on the GPU in a fairly
> transparent way (at least transparent to the user).
> 
> Cheers,
> 
> - Ross
> 
> 
> > -----Original Message-----
> > From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos-
> > users-bounces at software.sandia.gov] On Behalf Of Mark Hoemmen
> > Sent: Monday, August 02, 2010 12:25 PM
> > To: trilinos-users at software.sandia.gov
> > Subject: Re: [Trilinos-Users] Trilinos-Users Digest, Vol 60, Issue 1
> >
> > On Aug 1, 2010, at 10:08 PM, trilinos-users-
> request at software.sandia.gov
> > wrote:
> > > Message: 4
> > > Date: Mon, 02 Aug 2010 02:46:31 +0200
> > > From: Nico Schl?mer <nico.schloemer at ua.ac.be>
> > > Subject: Re: [Trilinos-Users] Epetra_SerialDenseVector vs.
> > >        Teuchos::SerialDenseVector
> > > To: "Bartlett, Roscoe A" <rabartl at sandia.gov>
> > > Cc: "Heroux, Michael A" <maherou at sandia.gov>, "Thornquist,
> Heidi
> > K"
> > >        <hkthorn at sandia.gov>, trilinos-users at software.sandia.gov
> > > Message-ID: <5a5040fba02ffca0981ca1e5c125a8d0 at ua.ac.be>
> > > Content-Type: text/plain; charset=utf-8
> > >
> > >> It is very hard to make operator+, operator-, operator* efficient.
> > >
> > > I see.
> > > Would you have any recommendation for me what to do with expression
> > like
> > >
> > >   y = alpha * x1 + beta * x2 + ...
> > >
> > > ?
> >
> > "Efficient" here means "not creating temporary vectors."  Each of
> those
> > "alpha*x1" terms will have to create a new temporary vector, and each
> > operator+ invocation will have to do so as well.  The temporaries
> will
> > go away, but you'll still have to spend time in memory allocation.
> >
> > If you're not worried about that, then you could define non-member
> > operator+, operator*, ... methods.  They don't need to belong to or
> be
> > friends of Teuchos::SerialDenseVector, because SerialDenseVector has
> an
> > operator[].  Each of these methods should create and return a new
> > SerialDenseVector.
> >
> > If you are worried about the cost of creating temporary vectors in
> such
> > expressions, but still want to write expressions in this way, you may
> > wish to investigate the uBLAS, which is in the Boost collection of
> C++
> > libraries.  See e.g., the overview at
> >
> >
> http://www.boost.org/doc/libs/1_43_0/libs/numeric/ublas/doc/overview.ht
> > m
> >
> > mfh
> >
> >
> >
> >
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> 
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