[petsc-users] (no subject)

[Li Luo]

Thank you very much! It looks forming an analytic Jacobian is the only
choice.

Best,
Li

On Mon, Dec 2, 2019 at 3:21 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Dec 2, 2019 at 4:04 AM Li Luo <li.luo at kaust.edu.sa> wrote:
>
>> Thank you for your reply.
>>
>> The matrix is small with only 67500 rows, but is relatively dense since a
>> second-order discontinuous Galerkin FEM is used, nonzeros=23,036,400.
>>
>
> This is very dense, 0.5% fill or 340 nonzeros per row.
>
>
>> The number of colors is 539 as shown by using -mat_fd_coloring_view:
>>
>
> Coloring is not appropriate for this matrix since you have enormous dense
> blocks (I am guessing). It could work if you statically
> condense them out or had a fast analytic Jacobian. With 540 colors, it
> takes 540 matvecs to generate the action of the Jacobian.
>
>   Thanks,
>
>      Matt
>
>
>> MatFDColoring Object: 64 MPI processes
>>   type not yet set
>>   Error tolerance=1.49012e-08
>>   Umin=1.49012e-06
>>   Number of colors=539
>>   Information for color 0
>>     Number of columns 1
>>       378
>>     Number of rows 756
>>       0 1188
>>       1 1188
>>       2 1188
>>       3 1188
>>       4 1188
>>       5 1188
>>       ...
>>
>> Is this normal?
>> When using MCFD, is there any difference using mpiaij and mpibaij?
>>
>> Best,
>> Li
>>
>> On Mon, Dec 2, 2019 at 10:03 AM Smith, Barry F. <bsmith at mcs.anl.gov>
>> wrote:
>>
>>>
>>>   How many colors is it requiring?   And how long is the
>>> MatGetColoring() taking? Are you running in parallel?  The MatGetColoring()
>>> MATCOLORINGSL uses a sequential coloring algorithm so if your matrix is
>>> large and parallel the coloring will take a long time. The parallel
>>> colorings are MATCOLORINGGREEDY and MATCOLORINGJP
>>>
>>>   Barry
>>>
>>>
>>> > On Dec 1, 2019, at 12:56 AM, Li Luo <li.luo at kaust.edu.sa> wrote:
>>> >
>>> > Dear Developers,
>>> >
>>> > I tried to use the multi-color finite-difference (MC-FD) method for
>>> constructing the Jacobians. However, I find it is very slow compared to the
>>> exact Jacobian.
>>> > My implementation of MC-FD Jacobian is posted below, would you please
>>> check whether I am correct? Anything missed? Thank you!
>>> >
>>> > ////////// Setup phase:
>>> >           MatStructure flag;
>>> >           ISColoring   iscoloring;
>>> >           ierr = MatGetColoring(Jac,MATCOLORINGSL,&iscoloring);
>>> >           ierr =
>>> MatFDColoringCreate(Jac,iscoloring,&this->matfdcoloring);
>>> >           ierr =
>>> MatFDColoringSetFunction(this->matfdcoloring,(PetscErrorCode
>>> (*)(void))__libmesh_petsc_snes_residual,(void *)this);
>>> >           ierr = MatFDColoringSetFromOptions(this->matfdcoloring);
>>> >           ierr = ISColoringDestroy(&iscoloring);
>>> >
>>> > //////////// Apply:
>>> >           ierr = MatZeroEntries(*jac);CHKERRQ(ierr);
>>> >           ierr =
>>> MatFDColoringApply(*jac,solver->matfdcoloring,x,msflag,snes);
>>> >
>>> > Best regards,
>>> > Li Luo
>>> >
>>> > This message and its contents, including attachments are intended
>>> solely for the original recipient. If you are not the intended recipient or
>>> have received this message in error, please notify me immediately and
>>> delete this message from your computer system. Any unauthorized use or
>>> distribution is prohibited. Please consider the environment before printing
>>> this email.
>>>
>>>
>>
>> --
>>
>> Postdoctoral Fellow
>> Extreme Computing Research Center
>> King Abdullah University of Science & Technology
>> https://sites.google.com/site/rolyliluo/
>>
>> ------------------------------
>> This message and its contents, including attachments are intended solely
>> for the original recipient. If you are not the intended recipient or have
>> received this message in error, please notify me immediately and delete
>> this message from your computer system. Any unauthorized use or
>> distribution is prohibited. Please consider the environment before printing
>> this email.
>
>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>


-- 

Postdoctoral Fellow
Extreme Computing Research Center
King Abdullah University of Science & Technology
https://sites.google.com/site/rolyliluo/

-- 

This message and its contents, including attachments are intended solely 
for the original recipient. If you are not the intended recipient or have 
received this message in error, please notify me immediately and delete 
this message from your computer system. Any unauthorized use or 
distribution is prohibited. Please consider the environment before printing 
this email.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20191202/42159d15/attachment-0001.html>