2:  #include <petscsys.h>

  4: /*@
  5:     PetscSplitOwnershipBlock - Given a global (or local) length determines a local
  6:         (or global) length via a simple formula. Splits so each processors local size
  7:         is divisible by the block size.

  9:    Collective on MPI_Comm (if N is PETSC_DECIDE)

 11:    Input Parameters:
 12: +    comm - MPI communicator that shares the object being divided
 13: .    bs - block size
 14: .    n - local length (or PETSC_DECIDE to have it set)
 15: -    N - global length (or PETSC_DECIDE)

 17:   Level: developer

 19:    Notes:
 20:      n and N cannot be both PETSC_DECIDE

 22:      If one processor calls this with N of PETSC_DECIDE then all processors
 23:      must, otherwise the program will hang.

 25: .seealso: PetscSplitOwnership()

 27: @*/
 28: PetscErrorCode  PetscSplitOwnershipBlock(MPI_Comm comm,PetscInt bs,PetscInt *n,PetscInt *N)
 29: {
 31:   PetscMPIInt    size,rank;

 34:   if (*N == PETSC_DECIDE && *n == PETSC_DECIDE) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Both n and N cannot be PETSC_DECIDE");

 36:   if (*N == PETSC_DECIDE) {
 37:     if (*n % bs != 0) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"local size %D not divisible by block size %D",*n,bs);
 38:     MPIU_Allreduce(n,N,1,MPIU_INT,MPI_SUM,comm);
 39:   } else if (*n == PETSC_DECIDE) {
 40:     PetscInt Nbs = *N/bs;
 41:     MPI_Comm_size(comm,&size);
 42:     MPI_Comm_rank(comm,&rank);
 43:     *n   = bs*(Nbs/size + ((Nbs % size) > rank));
 44:   }
 45:   return(0);
 46: }


 49: /*@
 50:     PetscSplitOwnership - Given a global (or local) length determines a local
 51:         (or global) length via a simple formula

 53:    Collective on MPI_Comm (if n or N is PETSC_DECIDE)

 55:    Input Parameters:
 56: +    comm - MPI communicator that shares the object being divided
 57: .    n - local length (or PETSC_DECIDE to have it set)
 58: -    N - global length (or PETSC_DECIDE)

 60:   Level: developer

 62:    Notes:
 63:      n and N cannot be both PETSC_DECIDE

 65:      If one processor calls this with n or N of PETSC_DECIDE then all processors
 66:      must. Otherwise, an error is thrown in debug mode while the program will hang
 67:      in optimized (i.e. configured --with-debugging=0) mode.

 69: .seealso: PetscSplitOwnershipBlock()

 71: @*/
 72: PetscErrorCode  PetscSplitOwnership(MPI_Comm comm,PetscInt *n,PetscInt *N)
 73: {
 75:   PetscMPIInt    size,rank;

 78:   if (*N == PETSC_DECIDE && *n == PETSC_DECIDE) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Both n and N cannot be PETSC_DECIDE\n  likely a call to VecSetSizes() or MatSetSizes() is wrong.\nSee http://www.mcs.anl.gov/petsc/documentation/faq.html#split");
 79: #if defined(PETSC_USE_DEBUG)
 80:   {
 81:     PetscMPIInt l[2],g[2];
 82:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
 83:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
 84:     MPI_Comm_size(comm,&size);
 85:     MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm);
 86:     if (g[0] && g[0] != size) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for local size");
 87:     if (g[1] && g[1] != size) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for global size");
 88:   }
 89: #endif

 91:   if (*N == PETSC_DECIDE) {
 92:     MPIU_Allreduce(n,N,1,MPIU_INT,MPI_SUM,comm);
 93:   } else if (*n == PETSC_DECIDE) {
 94:     MPI_Comm_size(comm,&size);
 95:     MPI_Comm_rank(comm,&rank);
 96:     *n   = *N/size + ((*N % size) > rank);
 97: #if defined(PETSC_USE_DEBUG)
 98:   } else {
 99:     PetscInt tmp;
100:     MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm);
101:     if (tmp != *N) SETERRQ3(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ,"Sum of local lengths %D does not equal global length %D, my local length %D\n  likely a call to VecSetSizes() or MatSetSizes() is wrong.\nSee http://www.mcs.anl.gov/petsc/documentation/faq.html#split",tmp,*N,*n);
102: #endif
103:   }
104:   return(0);
105: }