[petsc-users] Dense multiply Sparse

[Matthew Knepley]

On Fri, May 25, 2012 at 9:49 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> No, its not okay.
>
> I think MatGetArray needs to be removed. Pretty much any use of it is
> wrong. It is not even the right thing for dense matrices because they
> should be distributed differently than PETSc does now.
>
Without it, people cannot get directly to the AIJ data structure. No matter
how wrong it is,
it is a constant request. I would keep it in just to satisfy that large
number of petsc-maints.

   Matt

> On May 25, 2012 8:44 AM, "Hui Zhang" <mike.hui.zhang at hotmail.com> wrote:
>
>> A new question: can I use MatSetValues in the following way?
>>
>> MatGetArray(A,&a);
>> a[0]= 1;
>> MatSetValues(A,...);    /* in particular, is this allowed inside
>> GetArray/RestoreArray? */
>> MatRestoreArray(A,&a);
>>
>> Thanks!
>> Hui
>>
>> On May 14, 2012, at 2:29 PM, Barry Smith wrote:
>>
>> >
>> >   If B is 50% dense then store it in a dense format. It will be much
>> faster and the extra memory is minimal.  Even 30% dense.
>> >
>> >   Barry
>> >
>> > On May 14, 2012, at 5:13 AM, Hui Zhang wrote:
>> >
>> >> I have two matrices A and B stored in sparse format.  While A is
>> really sparse, B is relatively
>> >> dense (say non-zeros entries about 50%).  Now to multiply the two
>> matrices, among
>> >>
>> >>     A*B
>> >> or
>> >>    (B^T * A^T)^T
>> >>
>> >> which is better, or no big difference ?
>> >>
>> >> Thanks!
>> >>
>> >
>> >
>>
>>


-- 
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
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