On Oct 31, 2011, at 11:14 AM, Matthew Knepley wrote:
> On Mon, Oct 31, 2011 at 3:54 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> Matt,
>
> Won't you always want ADD_VALUES support? After all this is how finite
> element matrix assembly is done. Each element stiffness becomes one block in
> the batch and then they get added into the global matrix? How would one use
> the current batch routine with finite elements?
>
> Of course ADD_VALUES works. What does not work is calling it multiple times
> on the same matrix, for the reasons I stated.
Maybe you should change the manual page to make this whole business clear.
Currently one could interpret it in a variety of ways.
For example "Inserts many blocks of values into a matrix at once."
"Inserts" isn't really right
and "In the future, we may extend this routine to handle rectangular blocks,
and additive mode." What the hey is "additive mode"? I thought ADD_VALUES as
opposed to INSERT_VALUES.
and just say that it cannot be called multiply times before
MatAssemblyBegin/End ....
Barry
>
> Matt
>
>
> Barry
>
> On Oct 31, 2011, at 10:48 AM, Matthew Knepley wrote:
>
> > On Mon, Oct 31, 2011 at 12:31 PM, Fredrik Heffer Valdmanis <fredva at
> > ifi.uio.no> wrote:
> > 2011/10/30 Matthew Knepley <knepley at gmail.com>
> > On Sun, Oct 30, 2011 at 12:22 PM, Fredrik Heffer Valdmanis <fredva at
> > ifi.uio.no> wrote:
> > 2011/10/28 Matthew Knepley <knepley at gmail.com>
> > On Fri, Oct 28, 2011 at 10:24 AM, Fredrik Heffer Valdmanis <fredva at
> > ifi.uio.no> wrote:
> > Hi,
> >
> > I am working on integrating the new GPU based vectors and matrices into
> > FEniCS. Now, I'm looking at the possibility for getting some speedup during
> > finite element assembly, specifically when inserting the local element
> > matrix into the global element matrix. In that regard, I have a few
> > questions I hope you can help me out with:
> >
> > - When calling MatSetValues with a MATSEQAIJCUSP matrix as parameter, what
> > exactly is it that happens? As far as I can see, MatSetValues is not
> > implemented for GPU based matrices, neither is the mat->ops->setvalues set
> > to point at any function for this Mat type.
> >
> > Yes, MatSetValues always operates on the CPU side. It would not make sense
> > to do individual operations on the GPU.
> >
> > I have written batched of assembly for element matrices that are all the
> > same size:
> >
> >
> > http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatSetValuesBatch.html
> >
> > Thanks. I assume that the best way to use the batch function is to batch up
> > all element matrices and insert all with one function call? Or is it
> > recommended to split it up into several smaller batches?
> >
> > Right now, several batches does not work.For insertion to be efficient, you
> > should keep the matrices in COO
> > format, or convert them back. We do not do either right now. The idea is to
> > see if it ever matters for applications.
> >
> >
> > OK, thanks.
> >
> > Any estimate on when additive mode will be added to MatSetValuesBatch? As
> > it is now, this batch function is of limited use to us, as it forces us to
> > maintain an extra internal data structure to handle accumulation of numbers
> > that are inserted at the same indices in the matrix.
> >
> > I cannot understand what you need this for. All you need is the complete
> > list of element matrices.
> >
> > Any particular reason you chose not to support additive mode in this first
> > implementation? Are there any considerations I should be aware of?
> >
> > I said why above. It would require data structure changes and code support,
> > and we would need some level of user request for that.
> >
> > Matt
> >
> > Thanks,
> >
> > Fredrik
> >
> >
> >
> >
> > --
> > What most experimenters take for granted before they begin their
> > experiments is infinitely more interesting than any results to which their
> > experiments lead.
> > -- Norbert Wiener
>
>
>
>
> --
> What most experimenters take for granted before they begin their experiments
> is infinitely more interesting than any results to which their experiments
> lead.
> -- Norbert Wiener
