Re: [petsc-dev] Time-Steppers: how to stop and resume iterations at intermediate times?

[Alexis Marboeuf]

Hi Matt,
Thanks a lot for your answer. I am going to define a monitoring function. And I 
will adapt the time step with TSAdapt to ensure I hit the exact intermediate 
times I am interested in inside a TSSolve.
Best,
Alexis

De : Matthew Knepley 
Envoyé : mardi 18 octobre 2022 23:12
À : Alexis Marboeuf 
Cc : petsc-dev@mcs.anl.gov 
Objet : Re: [petsc-dev] Time-Steppers: how to stop and resume iterations at 
intermediate times?

On Tue, Oct 18, 2022 at 3:49 PM Alexis Marboeuf 
mailto:alexis.marbo...@hotmail.fr>> wrote:
Dear Petsc Team,
I am using a TS object to integrate my equation in time. I set the final time 
using TSSetMaxTime. My question is about a proper way to stop and resume 
iterations at intermediate times inside the TSSolve. I would like to stop when 
reaching exactly some given intermediate times, do some work (writing my 
intermediate solution for example) and then resume iterations.

The easiest way to do this I think is to just set a monitor, which will tell 
you what time it is. Just check the time, and perform your action.

  Thanks,

 Matt

Thanks a lot for your time and your help.
Best,
Alexis


--
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/

Re: [petsc-dev] [petsc-users] Regarding the status of MatSolve on GPUs

[Junchao Zhang]

Sherry,  sorry to ping you again for this issue.

--Junchao Zhang


On Tue, Oct 11, 2022 at 11:04 AM Junchao Zhang 
wrote:

> Hi, Sherry,
>   A petsc user wants to call MatSolve(mat, b, x) multiple times with
> different b on GPUs. In petsc, the code is like
>
> PetscScalar *bptr = NULL;
> VecGetArray(b, &bptr)
> pdgssvx3d(.., bptr, ..);
>
> Note VecGetArray() returns a host pointer. If vector b's latest data is on
> GPU, PETSc needs to do a device to host memory copy. Now we want to save
> this memory copy and directly pass b's device pointer (obtained
> via VecCUDAGetArray()) to superlu_dist. But I did not find a mechanism for
> me to tell superlu_dist that bptr is a device pointer.
> Do you have suggestions?
>
> Thanks
> On Thu, Oct 6, 2022 at 2:32 PM Sajid Ali 
> wrote:
>
>> Hi PETSc-developers,
>>
>> Does PETSc currently provide (either native or third party support) for
>> MatSolve that can be performed entirely on a GPU given a factored matrix?
>> i.e. a direct solver that would store the factors L and U on the device and
>> use the GPU to solve the linear system. It does not matter if the GPU is
>> not used for the factorization as we intend to solve the same linear system
>> for 100s of iterations and thus try to prevent GPU->CPU transfers for the
>> MatSolve phase.
>>
>> Currently, I've built PETSc@main (commit 9c433d, 10/03) with
>> superlu-dist@develop, both of which are configured with CUDA. With this,
>> I'm seeing that each call to PCApply/MatSolve involves one GPU->CPU
>> transfer. Is it possible to avoid this?
>>
>> Thank You,
>> Sajid Ali (he/him) | Research Associate
>> Scientific Computing Division
>> Fermi National Accelerator Laboratory
>> s-sajid-ali.github.io
>>
>