Actual source code: psplit.c
petsc-3.15.0 2021-03-30
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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 (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 (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 https://www.mcs.anl.gov/petsc/documentation/faq.html#split");
     79:   if (PetscDefined(USE_DEBUG)) {
     80:     PetscMPIInt l[2],g[2];
     81:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
     82:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
     83:     MPI_Comm_size(comm,&size);
     84:     MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm);
     85:     if (g[0] && g[0] != size) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for local size");
     86:     if (g[1] && g[1] != size) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for global size");
     87:   }

     89:   if (*N == PETSC_DECIDE) {
     90:     PetscInt64 m = *n, M;
     91:     MPIU_Allreduce(&m,&M,1,MPIU_INT64,MPI_SUM,comm);
     92:     if (M > PETSC_MAX_INT) SETERRQ1(comm,PETSC_ERR_INT_OVERFLOW,"Global size overflow %" PetscInt64_FMT ". You may consider ./configure PETSc with --with-64-bit-indices for the case you are running", M);
     93:     else *N = (PetscInt)M;
     94:   } else if (*n == PETSC_DECIDE) {
     95:     MPI_Comm_size(comm,&size);
     96:     MPI_Comm_rank(comm,&rank);
     97:     *n   = *N/size + ((*N % size) > rank);
     98:   } else if (PetscDefined(USE_DEBUG)) {
     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 https://www.mcs.anl.gov/petsc/documentation/faq.html#split",tmp,*N,*n);
    102:   }
    103:   return(0);
    104: }

    107: /*@
    108:     PetscSplitOwnershipEqual - Given a global (or local) length determines a local
    109:         (or global) length via a simple formula, trying to have all local lengths equal

    111:    Collective (if n or N is PETSC_DECIDE)

    113:    Input Parameters:
    114: +    comm - MPI communicator that shares the object being divided
    115: .    n - local length (or PETSC_DECIDE to have it set)
    116: -    N - global length (or PETSC_DECIDE)

    118:    Level: developer

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

    125:      n and N cannot be both PETSC_DECIDE

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

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

    133: @*/
    134: PetscErrorCode  PetscSplitOwnershipEqual(MPI_Comm comm,PetscInt *n,PetscInt *N)
    135: {
    137:   PetscMPIInt    size,rank;

    140:   if (*N == PETSC_DECIDE && *n == PETSC_DECIDE) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Both n and N cannot be PETSC_DECIDE");
    141:   if (PetscDefined(USE_DEBUG)) {
    142:     PetscMPIInt l[2],g[2];
    143:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
    144:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
    145:     MPI_Comm_size(comm,&size);
    146:     MPIU_Allreduce(l,g,2,MPI_INT,MPI_SUM,comm);
    147:     if (g[0] && g[0] != size) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for local size");
    148:     if (g[1] && g[1] != size) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"All processes must supply PETSC_DECIDE for global size");
    149:   }

    151:   if (*N == PETSC_DECIDE) {
    152:     PetscInt64 m = *n, M;
    153:     MPIU_Allreduce(&m,&M,1,MPIU_INT64,MPI_SUM,comm);
    154:     if (M > PETSC_MAX_INT) SETERRQ1(comm,PETSC_ERR_INT_OVERFLOW,"Global size overflow %" PetscInt64_FMT ". You may consider ./configure PETSc with --with-64-bit-indices for the case you are running", M);
    155:     else *N = (PetscInt)M;
    156:   } else if (*n == PETSC_DECIDE) {
    157:     MPI_Comm_size(comm,&size);
    158:     MPI_Comm_rank(comm,&rank);
    159:     *n = *N/size;
    160:     if (*N % size) {
    161:       if ((rank+1)*(*n+1)<=*N)  *n = *n+1;
    162:       else if (rank*(*n+1)<=*N) *n = *N-rank*(*n+1);
    163:       else *n = 0;
    164:     }
    165:   } else if (PetscDefined(USE_DEBUG)) {
    166:     PetscInt tmp;
    167:     MPIU_Allreduce(n,&tmp,1,MPIU_INT,MPI_SUM,comm);
    168:     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",tmp,*N,*n);
    169:   }
    170:   return(0);
    171: }