[petsc-users] dmda and structures

[Jed Brown]

Gideon Simpson <gideon.simpson at icloud.com> writes:

> I'm trying to use 1D DMDA's to manage distributed monte carlo computations, and I've got the following problem.  If I know, in advance, how many floating points are needed for each realization, everything is fine.  But, if I want to be able to set this at run time, I can't get it to work.  What I have is:
>
> typedef struct {
>   PetscScalar id;
>   PetscScalar *x;
> } Realization;
>
> then, in the main part of the code:
>
>   Realization *realization_array;
>   DM sim_data_da;
>   Vec sim_data_vec;
>
>   PetscInt xsize=10, realization_dof, i;
>   PetscOptionsGetInt(NULL, "-xsize", &xsize, NULL);
>
> realization_dof	  = xsize + 1;
>
>
>   DMDACreate1d(PETSC_COMM_WORLD,DMDA_BOUNDARY_NONE, batch_size, realization_dof, 0, NULL, &sim_data_da);
>   DMCreateGlobalVector(sim_data_da,&sim_data_vec);
>
>   DMDAVecGetArray(sim_data_da, sim_data_vec, & realization_array);

Vec can only hold PetscScalar, not pointers.

>   Up to this point, I have no problem, but, when I try to access
>   realization_array[i].x[j], I get memory errors.  Is this
>   fundamentally unworkable, or is there a fix?

You can't have this syntax in C or C++.  I suggest tiny accessor
functions that use the realization_dof to return the correct entries.
The simplest version would look like

  realization_access(ctx,realization_array,i)[j]

where ctx holds the block size and realization_array is just a plain
PetscScalar*.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 835 bytes
Desc: not available
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20131228/b1611383/attachment.pgp>