Actual source code: ex9.c
1: static char help[] = "Demonstrates use of VecCreateGhost().\n\n";
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: */
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>
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;
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");
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
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().
45: In this example we consider the vector as representing
46: degrees of freedom in a one dimensional grid with periodic
47: boundary conditions.
49: ----Processor 1--------- ----Processor 2 --------
50: 0 1 2 3 4 5 6 7 8 9 10 11
51: |----|
52: |-------------------------------------------------|
54: */
56: if (rank == 0) {
57: ifrom[0] = 11;
58: ifrom[1] = 6;
59: } else {
60: ifrom[0] = 0;
61: ifrom[1] = 5;
62: }
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: }
84: /*
85: Test VecDuplicate()
86: */
87: PetscCall(VecDuplicate(gxs, &gx));
88: PetscCall(VecDestroy(&gxs));
90: /*
91: Access the local representation
92: */
93: PetscCall(VecGhostGetLocalForm(gx, &lx));
95: /*
96: Set the values from 0 to 12 into the "global" vector
97: */
98: PetscCall(VecGetOwnershipRange(gx, &rstart, &rend));
99: for (i = rstart; i < rend; i++) {
100: value = (PetscScalar)i;
101: PetscCall(VecSetValues(gx, 1, &i, &value, INSERT_VALUES));
102: }
103: PetscCall(VecAssemblyBegin(gx));
104: PetscCall(VecAssemblyEnd(gx));
106: PetscCall(VecGhostUpdateBegin(gx, INSERT_VALUES, SCATTER_FORWARD));
107: PetscCall(VecGhostUpdateEnd(gx, INSERT_VALUES, SCATTER_FORWARD));
109: /*
110: Print out each vector, including the ghost padding region.
111: */
112: PetscCall(VecGetArray(lx, &array));
113: for (i = 0; i < nlocal + nghost; i++) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "%" PetscInt_FMT " %g\n", i, (double)PetscRealPart(array[i])));
114: PetscCall(VecRestoreArray(lx, &array));
115: PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT));
116: PetscCall(VecGhostRestoreLocalForm(gx, &lx));
118: /* Another test that sets ghost values and then accumulates onto the owning processors using MIN_VALUES */
119: if (flg3) {
120: if (rank == 0) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "\nTesting VecGhostUpdate with MIN_VALUES\n"));
121: PetscCall(VecGhostGetLocalForm(gx, &lx));
122: PetscCall(VecGetArray(lx, &array));
123: for (i = 0; i < nghost; i++) array[nlocal + i] = rank ? (PetscScalar)4 : (PetscScalar)8;
124: PetscCall(VecRestoreArray(lx, &array));
125: PetscCall(VecGhostRestoreLocalForm(gx, &lx));
127: PetscCall(VecGhostUpdateBegin(gx, MIN_VALUES, SCATTER_REVERSE));
128: PetscCall(VecGhostUpdateEnd(gx, MIN_VALUES, SCATTER_REVERSE));
130: PetscCall(VecGhostGetLocalForm(gx, &lx));
131: PetscCall(VecGetArray(lx, &array));
133: for (i = 0; i < nlocal + nghost; i++) PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "%" PetscInt_FMT " %g\n", i, (double)PetscRealPart(array[i])));
134: PetscCall(VecRestoreArray(lx, &array));
135: PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT));
136: PetscCall(VecGhostRestoreLocalForm(gx, &lx));
137: }
139: PetscCall(PetscOptionsHasName(NULL, NULL, "-vecghostgetghostis", &flg4));
140: if (flg4) {
141: PetscCall(VecGhostGetGhostIS(gx, &ghost));
142: PetscCall(ISView(ghost, PETSC_VIEWER_STDOUT_WORLD));
143: }
144: PetscCall(PetscOptionsHasName(NULL, NULL, "-getgtlmapping", &flg5));
145: if (flg5) {
146: PetscCall(VecGetLocalToGlobalMapping(gx, &mapping));
147: PetscCall(ISLocalToGlobalMappingView(mapping, NULL));
148: }
150: PetscCall(VecDestroy(&gx));
152: if (flg) PetscCall(PetscFree(tarray));
153: PetscCall(PetscFinalize());
154: return 0;
155: }
157: /*TEST
159: test:
160: nsize: 2
162: test:
163: suffix: 2
164: nsize: 2
165: args: -allocate
166: output_file: output/ex9_1.out
168: test:
169: suffix: 3
170: nsize: 2
171: args: -vecmpisetghost
172: output_file: output/ex9_1.out
174: test:
175: suffix: 4
176: nsize: 2
177: args: -minvalues
178: output_file: output/ex9_2.out
179: requires: !complex
181: test:
182: suffix: 5
183: nsize: 2
184: args: -vecghostgetghostis
186: test:
187: suffix: 6
188: nsize: 2
189: args: -getgtlmapping
191: TEST*/