Actual source code: psplit.c

      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 (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: {
     30:   PetscMPIInt    size,rank;

     34:   if (*N == PETSC_DECIDE) {
     36:     MPIU_Allreduce(n,N,1,MPIU_INT,MPI_SUM,comm);
     37:   } else if (*n == PETSC_DECIDE) {
     38:     PetscInt Nbs = *N/bs;
     39:     MPI_Comm_size(comm,&size);
     40:     MPI_Comm_rank(comm,&rank);
     41:     *n   = bs*(Nbs/size + ((Nbs % size) > rank));
     42:   }
     43:   return 0;
     44: }

     46: /*@
     47:     PetscSplitOwnership - Given a global (or local) length determines a local
     48:         (or global) length via a simple formula

     50:    Collective (if n or N is PETSC_DECIDE)

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

     57:   Level: developer

     59:    Notes:
     60:      n and N cannot be both PETSC_DECIDE

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

     66: .seealso: PetscSplitOwnershipBlock()

     68: @*/
     69: PetscErrorCode  PetscSplitOwnership(MPI_Comm comm,PetscInt *n,PetscInt *N)
     70: {
     71:   PetscMPIInt    size,rank;

     74:   if (PetscDefined(USE_DEBUG)) {
     75:     PetscMPIInt l[2],g[2];
     76:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
     77:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
     78:     MPI_Comm_size(comm,&size);
     79:     MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm);
     82:   }

     84:   if (*N == PETSC_DECIDE) {
     85:     PetscInt64 m = *n, M;
     86:     MPIU_Allreduce(&m,&M,1,MPIU_INT64,MPI_SUM,comm);
     88:     else *N = (PetscInt)M;
     89:   } else if (*n == PETSC_DECIDE) {
     90:     MPI_Comm_size(comm,&size);
     91:     MPI_Comm_rank(comm,&rank);
     92:     *n   = *N/size + ((*N % size) > rank);
     93:   } else if (PetscDefined(USE_DEBUG)) {
     94:     PetscInt tmp;
     95:     MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm);
     97:   }
     98:   return 0;
     99: }

    101: /*@
    102:     PetscSplitOwnershipEqual - Given a global (or local) length determines a local
    103:         (or global) length via a simple formula, trying to have all local lengths equal

    105:    Collective (if n or N is PETSC_DECIDE)

    107:    Input Parameters:
    108: +    comm - MPI communicator that shares the object being divided
    109: .    n - local length (or PETSC_DECIDE to have it set)
    110: -    N - global length (or PETSC_DECIDE)

    112:    Level: developer

    114:    Notes:
    115:      This is intended to be used with MATSCALAPACK, where the local size must
    116:      be equal in all processes (except possibly the last one). For instance,
    117:      the local sizes when spliting N=50 with 6 processes are 9,9,9,9,9,5

    119:      n and N cannot be both PETSC_DECIDE

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

    125: .seealso: PetscSplitOwnership(), PetscSplitOwnershipBlock()

    127: @*/
    128: PetscErrorCode  PetscSplitOwnershipEqual(MPI_Comm comm,PetscInt *n,PetscInt *N)
    129: {
    130:   PetscMPIInt    size,rank;

    133:   if (PetscDefined(USE_DEBUG)) {
    134:     PetscMPIInt l[2],g[2];
    135:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
    136:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
    137:     MPI_Comm_size(comm,&size);
    138:     MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm);
    141:   }

    143:   if (*N == PETSC_DECIDE) {
    144:     PetscInt64 m = *n, M;
    145:     MPIU_Allreduce(&m,&M,1,MPIU_INT64,MPI_SUM,comm);
    147:     else *N = (PetscInt)M;
    148:   } else if (*n == PETSC_DECIDE) {
    149:     MPI_Comm_size(comm,&size);
    150:     MPI_Comm_rank(comm,&rank);
    151:     *n = *N/size;
    152:     if (*N % size) {
    153:       if ((rank+1)*(*n+1)<=*N)  *n = *n+1;
    154:       else if (rank*(*n+1)<=*N) *n = *N-rank*(*n+1);
    155:       else *n = 0;
    156:     }
    157:   } else if (PetscDefined(USE_DEBUG)) {
    158:     PetscInt tmp;
    159:     MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm);
    161:   }
    162:   return 0;
    163: }