[petsc-users] A problem with MPI Derived Data Type and 'calloc'

[Alan Wei]

Dear all,
    I hope you're having a nice day. I have a further question on this
issue in 3D.
1, Following the idea of Dr. Brown and Dr. Knepley, I finished a 2D test,
which works very fine. Here, I did it in 3D by
"
    TESTVAR ***a, ***b, ***c;
    TESTVAR **aa, **bb, **cc;
    TESTVAR *arraya, *arrayb, *arrayc;

    arraya = (TESTVAR*) calloc(SIZE*SIZE*SIZE, sizeof(TESTVAR));
    arrayb = (TESTVAR*) calloc(SIZE*SIZE*SIZE, sizeof(TESTVAR));
    arrayc = (TESTVAR*) calloc(SIZE*SIZE*SIZE, sizeof(TESTVAR));

    aa =(TESTVAR**) calloc(SIZE*SIZE, sizeof(TESTVAR*));
    bb =(TESTVAR**) calloc(SIZE*SIZE, sizeof(TESTVAR*));
    cc =(TESTVAR**) calloc(SIZE*SIZE, sizeof(TESTVAR*));

    for(i = 0; i < SIZE*SIZE; i++) {
      aa[i] = &arraya[i*SIZE];
      bb[i] = &arrayb[i*SIZE];
      cc[i] = &arrayc[i*SIZE];
    }

    a =(TESTVAR***) calloc(SIZE*SIZE, sizeof(TESTVAR**));
    b =(TESTVAR***) calloc(SIZE*SIZE, sizeof(TESTVAR**));
    c =(TESTVAR***) calloc(SIZE*SIZE, sizeof(TESTVAR**));

    for(i = 0; i < SIZE; i++) {
      a[i] = &aa[i*SIZE];
      b[i] = &bb[i*SIZE];
      c[i] = &cc[i*SIZE];
    }
"
  It works. However, I wonder if there is any other good ideas for 3D
problem other than this kinda of 'two-layer' approach.

2, I have a little question on PETSc about 3D processor ordering. Does
PETSc have any function giving me the nodes/rank number of neighboring
nodes/ranks? Are those 'Application Ordering' functions applicable for my
case?

thanks,
Alan

On Fri, Apr 13, 2012 at 5:41 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Fri, Apr 13, 2012 at 17:38, Zhenglun (Alan) Wei <zhenglun.wei at gmail.com
> > wrote:
>
>>     I have a final question on it. Is it taken a lot of memory for doing
>> this? As I understand, pointers won't occupy many memories and it works
>> like an alias. It will not, to my limit knowledge, take much extra memory
>> by doing this.
>
>
> A pointer takes about as much space as a floating point value, so that
> array of pointers costs about 1*N compared to the N*N matrix.
>
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