1 static char help[] = "Demonstrates use of VecCreateGhost().\n\n"; 2 3 /* 4 Description: Ghost padding is one way to handle local calculations that 5 involve values from other processors. VecCreateGhost() provides 6 a way to create vectors with extra room at the end of the vector 7 array to contain the needed ghost values from other processors, 8 vector computations are otherwise unaffected. 9 */ 10 11 /* 12 Include "petscvec.h" so that we can use vectors. Note that this file 13 automatically includes: 14 petscsys.h - base PETSc routines petscis.h - index sets 15 petscviewer.h - viewers 16 */ 17 #include <petscvec.h> 18 19 int main(int argc, char **argv) 20 { 21 PetscMPIInt rank, size; 22 PetscInt nlocal = 6, nghost = 2, ifrom[2], i, rstart, rend; 23 PetscBool flg, flg2, flg3, flg4, flg5; 24 PetscScalar value, *array, *tarray = 0; 25 Vec lx, gx, gxs; 26 IS ghost; 27 ISLocalToGlobalMapping mapping; 28 29 PetscFunctionBeginUser; 30 PetscCall(PetscInitialize(&argc, &argv, (char *)0, help)); 31 PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank)); 32 PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size)); 33 PetscCheck(size == 2, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "Must run example with two processors"); 34 35 /* 36 Construct a two dimensional graph connecting nlocal degrees of 37 freedom per processor. From this we will generate the global 38 indices of needed ghost values 39 40 For simplicity we generate the entire graph on each processor: 41 in real application the graph would stored in parallel, but this 42 example is only to demonstrate the management of ghost padding 43 with VecCreateGhost(). 44 45 In this example we consider the vector as representing 46 degrees of freedom in a one dimensional grid with periodic 47 boundary conditions. 48 49 ----Processor 1--------- ----Processor 2 -------- 50 0 1 2 3 4 5 6 7 8 9 10 11 51 |----| 52 |-------------------------------------------------| 53 54 */ 55 56 if (rank == 0) { 57 ifrom[0] = 11; 58 ifrom[1] = 6; 59 } else { 60 ifrom[0] = 0; 61 ifrom[1] = 5; 62 } 63 64 /* 65 Create the vector with two slots for ghost points. Note that both 66 the local vector (lx) and the global vector (gx) share the same 67 array for storing vector values. 68 */ 69 PetscCall(PetscOptionsHasName(NULL, NULL, "-allocate", &flg)); 70 PetscCall(PetscOptionsHasName(NULL, NULL, "-vecmpisetghost", &flg2)); 71 PetscCall(PetscOptionsHasName(NULL, NULL, "-minvalues", &flg3)); 72 if (flg) { 73 PetscCall(PetscMalloc1(nlocal + nghost, &tarray)); 74 PetscCall(VecCreateGhostWithArray(PETSC_COMM_WORLD, nlocal, PETSC_DECIDE, nghost, ifrom, tarray, &gxs)); 75 } else if (flg2) { 76 PetscCall(VecCreate(PETSC_COMM_WORLD, &gxs)); 77 PetscCall(VecSetType(gxs, VECMPI)); 78 PetscCall(VecSetSizes(gxs, nlocal, PETSC_DECIDE)); 79 PetscCall(VecMPISetGhost(gxs, nghost, ifrom)); 80 } else { 81 PetscCall(VecCreateGhost(PETSC_COMM_WORLD, nlocal, PETSC_DECIDE, nghost, ifrom, &gxs)); 82 PetscCall(VecSet(gxs, 1.0)); 83 if (rank == 1) PetscCall(VecSetValueLocal(gxs, 0, 2.0, INSERT_VALUES)); 84 PetscCall(VecAssemblyBegin(gxs)); 85 PetscCall(VecAssemblyEnd(gxs)); 86 value = 0.0; 87 if (rank == 1) { 88 PetscCall(VecGetArray(gxs, &array)); 89 value = array[0]; 90 PetscCall(VecRestoreArray(gxs, &array)); 91 } 92 PetscCall(MPIU_Allreduce(MPI_IN_PLACE, &value, 1, MPIU_SCALAR, MPIU_SUM, PETSC_COMM_WORLD)); 93 PetscCheck(PetscIsCloseAtTolScalar(value, 2.0, PETSC_SMALL, PETSC_SMALL), PETSC_COMM_WORLD, PETSC_ERR_PLIB, "%g != 2.0", (double)PetscAbsScalar(value)); 94 } 95 96 /* 97 Test VecDuplicate() 98 */ 99 PetscCall(VecDuplicate(gxs, &gx)); 100 PetscCall(VecDestroy(&gxs)); 101 102 /* 103 Access the local representation 104 */ 105 PetscCall(VecGhostGetLocalForm(gx, &lx)); 106 107 /* 108 Set the values from 0 to 12 into the "global" vector 109 */ 110 PetscCall(VecGetOwnershipRange(gx, &rstart, &rend)); 111 for (i = rstart; i < rend; i++) { 112 value = (PetscScalar)i; 113 PetscCall(VecSetValues(gx, 1, &i, &value, INSERT_VALUES)); 114 } 115 PetscCall(VecAssemblyBegin(gx)); 116 PetscCall(VecAssemblyEnd(gx)); 117 118 PetscCall(VecGhostUpdateBegin(gx, INSERT_VALUES, SCATTER_FORWARD)); 119 PetscCall(VecGhostUpdateEnd(gx, INSERT_VALUES, SCATTER_FORWARD)); 120 121 /* 122 Print out each vector, including the ghost padding region. 123 */ 124 PetscCall(VecGetArray(lx, &array)); 125 for (i = 0; i < nlocal + nghost; i++) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "%" PetscInt_FMT " %g\n", i, (double)PetscRealPart(array[i]))); 126 PetscCall(VecRestoreArray(lx, &array)); 127 PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT)); 128 PetscCall(VecGhostRestoreLocalForm(gx, &lx)); 129 130 /* Another test that sets ghost values and then accumulates onto the owning processors using MIN_VALUES */ 131 if (flg3) { 132 if (rank == 0) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "\nTesting VecGhostUpdate with MIN_VALUES\n")); 133 PetscCall(VecGhostGetLocalForm(gx, &lx)); 134 PetscCall(VecGetArray(lx, &array)); 135 for (i = 0; i < nghost; i++) array[nlocal + i] = rank ? (PetscScalar)4 : (PetscScalar)8; 136 PetscCall(VecRestoreArray(lx, &array)); 137 PetscCall(VecGhostRestoreLocalForm(gx, &lx)); 138 139 PetscCall(VecGhostUpdateBegin(gx, MIN_VALUES, SCATTER_REVERSE)); 140 PetscCall(VecGhostUpdateEnd(gx, MIN_VALUES, SCATTER_REVERSE)); 141 142 PetscCall(VecGhostGetLocalForm(gx, &lx)); 143 PetscCall(VecGetArray(lx, &array)); 144 145 for (i = 0; i < nlocal + nghost; i++) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "%" PetscInt_FMT " %g\n", i, (double)PetscRealPart(array[i]))); 146 PetscCall(VecRestoreArray(lx, &array)); 147 PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT)); 148 PetscCall(VecGhostRestoreLocalForm(gx, &lx)); 149 } 150 151 PetscCall(PetscOptionsHasName(NULL, NULL, "-vecghostgetghostis", &flg4)); 152 if (flg4) { 153 PetscCall(VecGhostGetGhostIS(gx, &ghost)); 154 PetscCall(ISView(ghost, PETSC_VIEWER_STDOUT_WORLD)); 155 } 156 PetscCall(PetscOptionsHasName(NULL, NULL, "-getgtlmapping", &flg5)); 157 if (flg5) { 158 PetscCall(VecGetLocalToGlobalMapping(gx, &mapping)); 159 if (rank == 0) PetscCall(ISLocalToGlobalMappingView(mapping, NULL)); 160 } 161 162 PetscCall(VecDestroy(&gx)); 163 164 if (flg) PetscCall(PetscFree(tarray)); 165 PetscCall(PetscFinalize()); 166 return 0; 167 } 168 169 /*TEST 170 171 test: 172 nsize: 2 173 174 test: 175 suffix: 2 176 nsize: 2 177 args: -allocate 178 output_file: output/ex9_1.out 179 180 test: 181 suffix: 3 182 nsize: 2 183 args: -vecmpisetghost 184 output_file: output/ex9_1.out 185 186 test: 187 suffix: 4 188 nsize: 2 189 args: -minvalues 190 output_file: output/ex9_2.out 191 requires: !complex 192 193 test: 194 suffix: 5 195 nsize: 2 196 args: -vecghostgetghostis 197 198 test: 199 suffix: 6 200 nsize: 2 201 args: -getgtlmapping 202 203 TEST*/ 204