[petsc-users] Dense multiply Sparse

[Hui Zhang]

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!
>> 
> 
>