[petsc-users] Use of DMDAVecGetArrayF90 and DMDAVecRestoreArrayF90

[Matthew Knepley]

On Sat, Nov 21, 2015 at 7:47 AM, TAY wee-beng <zonexo at gmail.com> wrote:

>
> On 10/11/2015 8:47 PM, Matthew Knepley wrote:
>
> On Tue, Nov 10, 2015 at 6:30 AM, TAY wee-beng <zonexo at gmail.com> wrote:
>
>>
>> On 10/11/2015 8:27 PM, Matthew Knepley wrote:
>>
>> On Tue, Nov 10, 2015 at 3:27 AM, TAY wee-beng < <zonexo at gmail.com>
>> zonexo at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> Inside my subroutine, I need to access the DA variable cu_types_array
>>> frequently.
>>>
>>> So I need to call DMDAVecGetArrayF90 and DMDAVecRestoreArrayF90 before
>>> and after frequently.
>>>
>>> Is this necessary? Can I call DMDAVecGetArrayF90 at the start and only
>>> call DMDAVecRestoreArrayF90 towards the end, where I don't need to modify
>>> the values of cu_types_array anymore?
>>>
>>> Will this cause memory corruption?
>>>
>>
>> You cannot use any other vector operations before you have called Restore.
>>
>>
>> Hi,
>>
>> What do you mean by vector operations? I will just be doing some maths
>> operation to change the values in cu_types_array. Is that fine?
>>
>
> While you have the array, no other operation can change the values.
>
> Hi,
>
> Let me clarify this. I declare in this way:
>
> DM  da_cu_types
>
> Vec cu_types_local,cu_types_global
>
> PetscScalar,pointer :: cu_types_array(:,:,:)
>
> call
> DMDACreate3d(MPI_COMM_WORLD,DM_BOUNDARY_NONE,DM_BOUNDARY_NONE,DM_BOUNDARY_NONE,DMDA_STENCIL_STAR,(end_ijk_uniform(1)
> - sta_ijk_uniform(1) + 1),(end_ijk_uniform(2) - sta_ijk_uniform(2) + 1),&
>
> (end_ijk_uniform(3) - sta_ijk_uniform(3) +
> 1),PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,1,stencil_width_IIB,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,da_cu_types,ierr)
>
> call DMCreateGlobalVector(da_cu_types,cu_types_global,ierr)
>
> call DMCreateLocalVector(da_cu_types,cu_types_local,ierr)
>
> So when I need to change the values in DA variable cu_types, I call:
>
> call DMDAVecGetArrayF90(da_cu_types,cu_types_local,cu_types_array,ierr)
>
> .... math operations, changing the values of cu_types_array, such as:
>
> cu_types_array = 0.d0
>
> call DMDAVecRestoreArrayF90(da_cu_types,cu_types_local,cu_types_array,ierr)
>
> 1st of all, does these DMDAVecGetArrayF90 and DMDAVecRestoreArrayF90 take
> a lot of time, especially if I call them many times.
>

No.


> Next qn is whether if I can call DMDAVecGetArrayF90 at the start, and
> DMDAVecRestoreArrayF90 after operations similar to the one above is
> finished.
>

You cannot do other Vec operations before you call Restore.

  Matt


> Thanks.
>
>
>    Matt
>
>
>>
>>
>> Also, must the array be restored using DMDAVecRestoreArrayF90 before
>>> calling DMLocalToLocalBegin,DMLocalToLocalEnd?
>>
>>
>> Yes.
>>
>>   Matt
>>
>>
>>>
>>> --
>>> Thank you.
>>>
>>> Yours sincerely,
>>>
>>> TAY wee-beng
>>>
>>>
>>
>>
>> --
>> 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
>>
>>
>>
>
>
> --
> 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
>
>
>


-- 
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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