[petsc-users] a question about PetscSectionCreate

[Matthew Knepley]

On Sun, May 28, 2017 at 1:49 AM, Dave May <dave.mayhem23 at gmail.com> wrote:

>
> On Sun, 28 May 2017 at 08:31, leejearl <leejearl at 126.com> wrote:
>
>> Hi, PETSc developer:
>>
>>      I need to create a PetscSection with a struct. The struct is
>> defined as follow,
>>
>>     typedef struct
>>     {
>>        PetscReal x;
>>        PetscInt id;
>>     } testStruct;
>>
>>     When I run the program, I got a wrong output as follow,
>>
>>     Vec Object: 1 MPI processes
>>    type: seq
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>> 2.
>> 4.94066e-324
>>
>> But when I defined the struct as
>>
>>     typedef struct
>>     {
>>        PetscReal x;
>>        PetscReal id;
>>     } testStruct;
>>
>> The output is ok. It seems that  there is some wrong with the memories
>> when I define the "id" as a PetscInt type.
>
>
> Yep.
>
>
>>
>> I can not find out the reasons, and any one can help me with it?
>
>
> The Vec object can only store quantities of type PetscScalar. It cannot
> store PetscInt's and it definitely cannot represent a mixture of
> PetscReal's and PetscInt's.
>

Dave is correct. However this usage completely misses the point of Section.
Section is a device for storing indices into
ANY storage, not just Vec and IS. I would manage an array of the structs
that I allocate, and use the Section to index into.

   Matt


>
> Thanks,
>  Dave
>
> The
>> source file "test.c" is attached.
>>
>>
>> Thanks,
>>
>> leejearl
>>
>>


-- 
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

http://www.caam.rice.edu/~mk51/
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