[petsc-users] question about DA

[Barry Smith]

  You cannot just split a 2d array among some processes and a 3d array across the same processes and expect somehow that the layouts of two of the indices will match between the two arrays.

  You can run, for example with -da_view to see how they two arrays are being laid out in parallel by default. You will need set certain values in the m,n, and p arguments to DMDACreate2d() and 3d to get layouts that match. Note that these are not the M,N, and P arguments.

   Barry


On Aug 27, 2011, at 4:09 PM, Likun Tan wrote:

> the size of temp and H is 9*9*201, the size of S is 9*9.
> 
> I used 2 processors, the returned values are
> temp: 0 0 0 9 9 101
> temp: 0 0 101 9 9 100
> H: 0 0 101 9 9 100
> S: 0 5 101 9 4 100
> 
> I am not sure what you mean by how DAs were constructed, the command i
> used for construction is:
> DACreate2d(PETSC_COMM_WORLD, DA_NONPERIODIC, DA_STENCIL_STAR, 9, 9,
> PETSC_DECIDE, PETSC_DECIDE, 1, 0, PETSC_NULL, PETSC_NULL, &da2D);
> DACreate3d(PETSC_COMM_WORLD, DA_NONPERIODIC, DA_STENCIL_STAR, 9, 9, 201,
> PETSC_DECIDE, PETSC_DECIDE, PETSC_DECIDE, 1, 0, PETSC_NULL, PETSC_NULL,
> PETSC_NULL, &da3D);
> 
> i got some sense of the problem after watching m, n, p, but i don't know
> how to avoid it.
> 
> On Sat, August 27, 2011 4:53 pm, Jed Brown wrote:
>> On Sat, Aug 27, 2011 at 15:49, Likun Tan <likunt at andrew.cmu.edu> wrote:
>> 
>> 
>>> I attached my code again, p was used in defining temp and H, when
>>> defining S, we don't need p and zs:
>>> 
>>> 
>> 
>> You need p to know the limits of the integral. You need that the domain
>> not be decomposed in the z direction if you are going to integrate without
>> doing communication. You still haven't shown us how the DAs were
>> constructed or what the returned values for (xs,ys,zs,m,n,p) were when got
>> them from da3D and what (xs,ys,m,n) were when you got them from da2D.
>> 
> 
> 
> 
>