Actual source code: psplit.c

petsc-3.14.6 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: }