[petsc-users] PETSC address vector c++ access

[RAELI ALICE]

Thank you so much Matt and Dave,
we will test soon. I think they are what we were searching 
for.

Alice

On Fri, 30 Nov 2018 19:40:34 +0000
  Dave May <dave.mayhem23 at gmail.com> wrote:
> On Fri, 30 Nov 2018 at 14:50, RAELI ALICE via 
>petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> 
>> Hi All,
>> My team is working on a PETSC version of an existent 
>>code.
>> In order to convert the main part of this work retaining 
>>the c++ levels of
>> abstraction,
>> we would access to c++ vector data structures easily.
>>
>> We would like to use the memory area allocated using c++ 
>>as a Petsc Vector
>>
>> a supposed pseudocode could be:
>>
>>
>> *int data[] = { 1,2,3,4,5,6,7,8,9 };*
>>
> 
> To avoid any confusion (or disappointment) later, I want 
>to point out that
> your pseudo code is wrong (specifically the line above) 
>and in detail would
> result in a SEGV.
> 
> A PETSc Vec object can ONLY represent PetscScalar data 
>types.
> 
> It may well have been a typo on your part, but I think 
>it's important to
> emphasise that the Vec object does not try to mimic a 
>C++ template with the
> data type as an argument.
> 
> Thanks,
>  Dave
> 
> 
>>
>>
>> *unsigned int sizeVectorPetsC = data.size();Vec v(data, 
>>sizeVectorPetsC);
>> (Can it exists with easy access petsc routines?)*
>> *cout<< "The mapped vector v is: [";*
>>
>> *    PetscScalar *vecArray;*
>>
>>
>>
>>
>>
>>
>> *PetscGetArray(v, &array);for (unsigned int i = 0; i < 
>>sizeVectorPetsC;
>> i++){Informations of v are the informations of 
>>data.(same memory read by
>> both data structures)}PetscRestoreArray(v,&array);*
>> * cout<< "]"<< endl;*
>>
>>
>> Is it provided this kind of duality between c++ and 
>>Petsc objects without
>> a re-copy of the concerned informations?
>>
>> Thank you,
>> Alice
>>
>Yes, I think you want

>  https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecCreateSeqWithArray.html
>  https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecCreateMPIWithArray.html#VecCreateMPIWithArray
>
>and you can even do advanced things with the storage
>
>  https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecPlaceArray.html#VecPlaceArray
>
>but you need to be more careful.
>
>Let me know if this does not do what you wanted.
>
>  Thanks,
>
>     Matt
> 
>
>>   Thank you,
>>    Alice