Actual source code: psplit.c

petsc-3.8.2 2017-11-09
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  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 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 of PETSC_DECIDE then all processors
 66:      must, otherwise the program will hang.

 68: .seealso: PetscSplitOwnershipBlock()

 70: @*/
 71: PetscErrorCode  PetscSplitOwnership(MPI_Comm comm,PetscInt *n,PetscInt *N)
 72: {
 74:   PetscMPIInt    size,rank;

 77:   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 (*N == PETSC_DECIDE) {
 80:     MPIU_Allreduce(n,N,1,MPIU_INT,MPI_SUM,comm);
 81:   } else if (*n == PETSC_DECIDE) {
 82:     MPI_Comm_size(comm,&size);
 83:     MPI_Comm_rank(comm,&rank);
 84:     *n   = *N/size + ((*N % size) > rank);
 85: #if defined(PETSC_USE_DEBUG)
 86:   } else {
 87:     PetscInt tmp;
 88:     MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm);
 89:     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);
 90: #endif
 91:   }
 92:   return(0);
 93: }