1: #include <petscsys.h>

  3: /*@
  4:   PetscSplitOwnershipBlock - Given a global (or local) length determines a local
  5:   (or global) length via a simple formula. Splits so each processors local size
  6:   is divisible by the block size.

  8:   Collective (if `N` is `PETSC_DECIDE`)

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

 16:   Level: developer

 18:   Notes:
 19:   `n` and `N` cannot be both `PETSC_DECIDE`

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

 24: .seealso: `PetscSplitOwnership()`, `PetscSplitOwnershipEqual()`
 25: @*/
 26: PetscErrorCode PetscSplitOwnershipBlock(MPI_Comm comm, PetscInt bs, PetscInt *n, PetscInt *N)
 27: {
 28:   PetscMPIInt size, rank;

 30:   PetscFunctionBegin;
 31:   PetscCheck(*N != PETSC_DECIDE || *n != PETSC_DECIDE, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Both n and N cannot be PETSC_DECIDE");

 33:   if (*N == PETSC_DECIDE) {
 34:     PetscCheck(*n % bs == 0, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "local size %" PetscInt_FMT " not divisible by block size %" PetscInt_FMT, *n, bs);
 35:     PetscCallMPI(MPIU_Allreduce(n, N, 1, MPIU_INT, MPI_SUM, comm));
 36:   } else if (*n == PETSC_DECIDE) {
 37:     PetscInt Nbs = *N / bs;
 38:     PetscCallMPI(MPI_Comm_size(comm, &size));
 39:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
 40:     *n = bs * (Nbs / size + ((Nbs % size) > rank));
 41:   }
 42:   PetscFunctionReturn(PETSC_SUCCESS);
 43: }

 45: /*@
 46:   PetscSplitOwnership - Given a global (or local) length determines a local
 47:   (or global) length via a simple formula

 49:   Collective (if `n` or `N` is `PETSC_DECIDE` or `PETSC_DETERMINE`)

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

 56:   Level: developer

 58:   Notes:
 59:   `n` and `N` cannot be both `PETSC_DECIDE` and `PETSC_DETERMINE`

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

 65: .seealso: `PetscSplitOwnershipBlock()`, `PetscSplitOwnershipEqual()`, `PETSC_DECIDE`, `PETSC_DETERMINE`
 66: @*/
 67: PetscErrorCode PetscSplitOwnership(MPI_Comm comm, PetscInt *n, PetscInt *N)
 68: {
 69:   PetscMPIInt size, rank;

 71:   PetscFunctionBegin;
 72:   PetscCheck(*N != PETSC_DECIDE || *n != PETSC_DECIDE, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Both n and N cannot be PETSC_DECIDE, likely a call to VecSetSizes() or MatSetSizes() is wrong. See https://petsc.org/release/faq/#split-ownership");
 73:   if (PetscDefined(USE_DEBUG)) {
 74:     PetscMPIInt l[2], g[2];
 75:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
 76:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
 77:     PetscCallMPI(MPI_Comm_size(comm, &size));
 78:     PetscCallMPI(MPIU_Allreduce(l, g, 2, MPI_INT, MPI_SUM, comm));
 79:     PetscCheck(!g[0] || g[0] == size, comm, PETSC_ERR_ARG_INCOMP, "All processes must supply PETSC_DECIDE for local size");
 80:     PetscCheck(!g[1] || g[1] == size, comm, PETSC_ERR_ARG_INCOMP, "All processes must supply PETSC_DECIDE for global size");
 81:   }

 83:   if (*N == PETSC_DECIDE) {
 84:     PetscCallMPI(MPIU_Allreduce(n, N, 1, MPIU_INT, MPI_SUM, comm));
 85:   } else if (*n == PETSC_DECIDE) {
 86:     PetscCallMPI(MPI_Comm_size(comm, &size));
 87:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
 88:     *n = *N / size + ((*N % size) > rank);
 89:   } else if (PetscDefined(USE_DEBUG)) {
 90:     PetscInt tmp;
 91:     PetscCallMPI(MPIU_Allreduce(n, &tmp, 1, MPIU_INT, MPI_SUM, comm));
 92:     PetscCheck(tmp == *N, PETSC_COMM_SELF, PETSC_ERR_ARG_SIZ, "Sum of local lengths %" PetscInt_FMT " does not equal global length %" PetscInt_FMT ", my local length %" PetscInt_FMT ", likely a call to VecSetSizes() or MatSetSizes() is wrong. See https://petsc.org/release/faq/#split-ownership", tmp, *N, *n);
 93:   }
 94:   PetscFunctionReturn(PETSC_SUCCESS);
 95: }

 97: /*@
 98:   PetscSplitOwnershipEqual - Given a global (or local) length determines a local
 99:   (or global) length via a simple formula, trying to have all local lengths equal

101:   Collective (if `n` or `N` is `PETSC_DECIDE`)

103:   Input Parameters:
104: + comm - MPI communicator that shares the object being divided
105: . n    - local length (or `PETSC_DECIDE` to have it set)
106: - N    - global length (or `PETSC_DECIDE`)

108:   Level: developer

110:   Notes:
111:   This is intended to be used with `MATSCALAPACK`, where the local size must
112:   be equal in all processes (except possibly the last one). For instance,
113:   the local sizes when splitting `N`=50 with 6 processes are 9,9,9,9,9,5

115:   n and N cannot be both `PETSC_DECIDE`

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

121: .seealso: `PetscSplitOwnership()`, `PetscSplitOwnershipBlock()`
122: @*/
123: PetscErrorCode PetscSplitOwnershipEqual(MPI_Comm comm, PetscInt *n, PetscInt *N)
124: {
125:   PetscMPIInt size, rank;

127:   PetscFunctionBegin;
128:   PetscCheck(*N != PETSC_DECIDE || *n != PETSC_DECIDE, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Both n and N cannot be PETSC_DECIDE");
129:   if (PetscDefined(USE_DEBUG)) {
130:     PetscMPIInt l[2], g[2];
131:     l[0] = (*n == PETSC_DECIDE) ? 1 : 0;
132:     l[1] = (*N == PETSC_DECIDE) ? 1 : 0;
133:     PetscCallMPI(MPI_Comm_size(comm, &size));
134:     PetscCallMPI(MPIU_Allreduce(l, g, 2, MPI_INT, MPI_SUM, comm));
135:     PetscCheck(!g[0] || g[0] == size, comm, PETSC_ERR_ARG_INCOMP, "All processes must supply PETSC_DECIDE for local size");
136:     PetscCheck(!g[1] || g[1] == size, comm, PETSC_ERR_ARG_INCOMP, "All processes must supply PETSC_DECIDE for global size");
137:   }

139:   if (*N == PETSC_DECIDE) {
140:     PetscCallMPI(MPIU_Allreduce(n, N, 1, MPIU_INT, MPI_SUM, comm));
141:   } else if (*n == PETSC_DECIDE) {
142:     PetscCallMPI(MPI_Comm_size(comm, &size));
143:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
144:     *n = *N / size;
145:     if (*N % size) {
146:       if ((rank + 1) * (*n + 1) <= *N) *n = *n + 1;
147:       else if (rank * (*n + 1) <= *N) *n = *N - rank * (*n + 1);
148:       else *n = 0;
149:     }
150:   } else if (PetscDefined(USE_DEBUG)) {
151:     PetscInt tmp;
152:     PetscCallMPI(MPIU_Allreduce(n, &tmp, 1, MPIU_INT, MPI_SUM, comm));
153:     PetscCheck(tmp == *N, PETSC_COMM_SELF, PETSC_ERR_ARG_SIZ, "Sum of local lengths %" PetscInt_FMT " does not equal global length %" PetscInt_FMT ", my local length %" PetscInt_FMT, tmp, *N, *n);
154:   }
155:   PetscFunctionReturn(PETSC_SUCCESS);
156: }