[petsc-users] Row Orderings of Mat and Vec

[Barry Smith]

On Feb 1, 2012, at 5:02 AM, Hui Zhang wrote:

> 
> On Jan 31, 2012, at 1:23 PM, Jed Brown wrote:
> 
>> On Tue, Jan 31, 2012 at 04:11, Hui Zhang <mike.hui.zhang at hotmail.com> wrote:
>> Suppose using MatCreate() and MatSetSizes() we obtain a Mat A, and then
>> tion and then using local indices (e.g. MatSetValuesLocal()) during assembly. You might use AO for that setup step, but it usually doesn't make sense to use _during_ assembly.
> 
> thanks, do you mean that it is faster to use LocaltoGlobalMapping & SetValuesLocal
> than to use AO & SetValues globally? Is there a big difference in performance?

   Yes, using the SetValuesLocal approach will be much faster for large problems than using the AO to map to global indices and calling SetValues.

   Barry

> 
> 
>>  
>> with
>> P_1 the permutation corresponding to ao_1.  In a similar way, we have that b
>> becomes P_2 b under the petsc ordering.  I want to make sure P_1 and P_2 are
>> the same so arises my question.
>> 
>> Thanks a lot!
>> Hui
>> 
>> 
>> 
>