[petsc-users] petsc malloc multidimensional array

[吕超]

  Many thanks for all your explanation, its really help me!

  Now my program run smoothly, and the result is satisfactory!

  For 3d results, I now make drawings by many slices in matlab.

  And I find it not visualized, so could do you please tell me how can I draw these 3d space fileds finely?


> -----原始邮件-----
> 发件人: "Jed Brown" <jed at jedbrown.org>
> 发送时间: 2014年3月12日 星期三
> 收件人: "Barry Smith" <bsmith at mcs.anl.gov>, "Matthew Knepley" <knepley at gmail.com>
> 抄送: "吕超" <luchao at mail.iggcas.ac.cn>, petsc-users <petsc-users at mcs.anl.gov>
> 主题: Re: [petsc-users] petsc malloc multidimensional array
> 
> Barry Smith <bsmith at mcs.anl.gov> writes:
> 
> > On Mar 11, 2014, at 9:22 AM, Matthew Knepley <knepley at gmail.com> wrote:
> >
> >> 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.
> >
> >    If the 512 is a fixed number, not different for different elements you can in C 89 standard use 
> >
> >     mysubroutine(….)
> >     double element[512][512];
> 
> This is fairly "big" -- 2 MiB of what is typically an 8 MiB stack size,
> so if you allocate several of these, you may get a stack overflow.  You
> can increase the stack size on most systems, but that makes it more
> complicated to run your program.  I would allocate dynamically if you
> are worried about this.
> 
> If you want to avoid PETSc array functions, you can allocate dynamically
> and access via a pointer:
> 
>   double *mem = malloc(M*N*sizeof(double));
>   double (*p)[N] = (double (*)[N])mem;
>   // access p[i][j]
>   free(mem);



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