[petsc-users] petsc malloc multidimensional array

[Matthew Knepley]

On Tue, Mar 11, 2014 at 9:05 AM, 吕超 <luchao at mail.iggcas.ac.cn> wrote:

> Hi, Matthew:
>
>      Thank you for your reply so fast! but I also have some questions:
>
>     2d arrays I used is just intermediate variable, not for fields, and
> the fields is used Vector. In Finite element method, when I use element
> stiffness matrix to assemble global stiffness matrix, I always first
> compute the 2d element stiffness matrixs whose size is 512*512(inner points
> in element),so big for static arrays. So i want to use PetscMalloc to bulid
> 2d arrays to store element stiffness matrixs' values. And I don't know how
> to do, could do tell me?
>
AGAIN, these are C questions. You could

  a) malloc() each row

  b) malloc() the whole thing, and make pointers to each row

Notice that this is enormous for an element matrix. This is likely not
optimal for performance.

   Matt


>      then use another 1d array to abstract the nonzero values from 2d
> arrays above-mentioned. could do you please tell me  some other methods
> much more convenient and faster?
>
>
> -----原始邮件-----
> *发件人:* "Matthew Knepley" <knepley at gmail.com>
> *发送时间:* 2014年3月11日 星期二
> *收件人:* "吕超" <luchao at mail.iggcas.ac.cn>
> *抄送:* petsc-users <petsc-users at mcs.anl.gov>
> *主题:* Re: [petsc-users] petsc malloc multidimensional array
>
> On Tue, Mar 11, 2014 at 8:37 AM, 吕超 <luchao at mail.iggcas.ac.cn> wrote:
>
>>   Hi, recently,when I use PETSc to bulid 2d arrays such as PetscScalar
>> A[512][512],B[512][512],C,D,E,F,..., program always has error of
>> Segmentation Violation. So I want to use PetscMalloc to bulid 2d array, and
>> I hope that I can also use these 2d array A[i][j] by subscripts as before.
>> Could do please tell me how can I do? Thank you.
>>
> 1) This is a C question, not a PETSc question
>
> 2) If you are using 2D arrays for fields, you should be using the DMDA,
> which has a section in the manual
>
>   Thanks,
>
>      Matt
>
>
>> LV CHAO
>>
>> 2014/3/11
>>
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>
>
> --
> 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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>
>
>


-- 
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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