Actual source code: dasub.c

  1: #define PETSCDM_DLL

  3: /*
  4:   Code for manipulating distributed regular arrays in parallel.
  5: */

 7:  #include src/dm/da/daimpl.h

 11: /*@C
 12:    DAGetProcessorSubset - Returns a communicator consisting only of the
 13:    processors in a DA that own a particular global x, y, or z grid point
 14:    (corresponding to a logical plane in a 3D grid or a line in a 2D grid).

 16:    Collective on DA

 18:    Input Parameters:
 19: +  da - the distributed array
 20: .  dir - Cartesian direction, either DA_X, DA_Y, or DA_Z
 21: -  gp - global grid point number in this direction

 23:    Output Parameters:
 24: .  comm - new communicator

 26:    Level: advanced

 28:    Notes:
 29:    All processors that share the DA must call this with the same gp value

 31:    This routine is particularly useful to compute boundary conditions
 32:    or other application-specific calculations that require manipulating
 33:    sets of data throughout a logical plane of grid points.

 35: .keywords: distributed array, get, processor subset
 36: @*/
 37: PetscErrorCode PETSCDM_DLLEXPORT DAGetProcessorSubset(DA da,DADirection dir,PetscInt gp,MPI_Comm *comm)
 38: {
 39:   MPI_Group      group,subgroup;
 41:   PetscInt       i,ict,flag,*owners,xs,xm,ys,ym,zs,zm;
 42:   PetscMPIInt    size,*ranks;

 46:   flag = 0;
 47:   DAGetCorners(da,&xs,&xm,&ys,&ym,&zs,&zm);
 48:   MPI_Comm_size(da->comm,&size);
 49:   if (dir == DA_Z) {
 50:     if (da->dim < 3) SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"DA_Z invalid for DA dim < 3");
 51:     if (gp < 0 || gp > da->P) SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"invalid grid point");
 52:     if (gp >= zs && gp < zs+zm) flag = 1;
 53:   } else if (dir == DA_Y) {
 54:     if (da->dim == 1) SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"DA_Y invalid for DA dim = 1");
 55:     if (gp < 0 || gp > da->N) SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"invalid grid point");
 56:     if (gp >= ys && gp < ys+ym) flag = 1;
 57:   } else if (dir == DA_X) {
 58:     if (gp < 0 || gp > da->M) SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"invalid grid point");
 59:     if (gp >= xs && gp < xs+xm) flag = 1;
 60:   } else SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"Invalid direction");

 62:   PetscMalloc2(size,PetscInt,&owners,size,PetscMPIInt,&ranks);
 63:   MPI_Allgather(&flag,1,MPIU_INT,owners,1,MPIU_INT,da->comm);
 64:   ict  = 0;
 65:   PetscLogInfo((da,"DAGetProcessorSubset: dim=%D, direction=%d, procs: ",da->dim,(int)dir));
 66:   for (i=0; i<size; i++) {
 67:     if (owners[i]) {
 68:       ranks[ict] = i; ict++;
 69:       PetscLogInfo((da,"%D ",i));
 70:     }
 71:   }
 72:   PetscLogInfo((da,"\n"));
 73:   MPI_Comm_group(da->comm,&group);
 74:   MPI_Group_incl(group,ict,ranks,&subgroup);
 75:   MPI_Comm_create(da->comm,subgroup,comm);
 76:   PetscFree2(owners,ranks);
 77:   return(0);
 78: }