Actual source code: ex8.c
1: /*$Id: ex8.c,v 1.28 2001/08/07 03:04:42 balay Exp $*/
2:
3: static char help[] = "Demonstrates generating a slice from a DA Vector.nn";
5: #include petscda.h
6: #include petscsys.h
7: #include petscao.h
9: /*
10: Given a DA generates a VecScatter context that will deliver a slice
11: of the global vector to each processor. In this example, each processor
12: receives the values i=*, j=*, k=rank, i.e. one z plane.
14: Note: This code is written assuming only one degree of freedom per node.
15: For multiple degrees of freedom per node use ISCreateBlock()
16: instead of ISCreateGeneral().
17: */
18: int GenerateSliceScatter(DA da,VecScatter *scatter,Vec *vslice)
19: {
20: AO ao;
21: int M,N,P,nslice,rank,*sliceindices,count,ierr,i,j;
22: MPI_Comm comm;
23: Vec vglobal;
24: IS isfrom,isto;
26: PetscObjectGetComm((PetscObject)da,&comm);
27: MPI_Comm_rank(comm,&rank);
29: DAGetAO(da,&ao);
30: DAGetInfo(da,0,&M,&N,&P,0,0,0,0,0,0,0);
32: /*
33: nslice is number of degrees of freedom in this processors slice
34: if there are more processors then z plans the extra processors get 0
35: elements in their slice.
36: */
37: if (rank < P) {nslice = M*N;} else nslice = 0;
39: /*
40: Generate the local vector to hold this processors slice
41: */
42: VecCreateSeq(PETSC_COMM_SELF,nslice,vslice);
43: DACreateGlobalVector(da,&vglobal);
45: /*
46: Generate the indices for the slice in the "natural" global ordering
47: Note: this is just an example, one could select any subset of nodes
48: on each processor. Just list them in the global natural ordering.
50: */
51: PetscMalloc((nslice+1)*sizeof(int),&sliceindices);
52: count = 0;
53: if (rank < P) {
54: for (j=0; j<N; j++) {
55: for (i=0; i<M; i++) {
56: sliceindices[count++] = rank*M*N + j*M + i;
57: }
58: }
59: }
60: /*
61: Convert the indices to the "PETSc" global ordering
62: */
63: AOApplicationToPetsc(ao,nslice,sliceindices);
64:
65: /* Create the "from" and "to" index set */
66: /* This is to scatter from the global vector */
67: ISCreateGeneral(PETSC_COMM_SELF,nslice,sliceindices,&isfrom);
68: /* This is to gather into the local vector */
69: ISCreateStride(PETSC_COMM_SELF,nslice,0,1,&isto);
71: VecScatterCreate(vglobal,isfrom,*vslice,isto,scatter);
73: ISDestroy(isfrom);
74: ISDestroy(isto);
76: PetscFree(sliceindices);
77: return 0;
78: }
81: int main(int argc,char **argv)
82: {
83: int rank,M = 3,N = 5,P=3,s=1;
84: int m = PETSC_DECIDE,n = PETSC_DECIDE,p = PETSC_DECIDE,ierr;
85: int *lx = PETSC_NULL,*ly = PETSC_NULL,*lz = PETSC_NULL;
86: PetscTruth flg;
87: DA da;
88: Vec local,global,vslice;
89: PetscScalar value;
90: DAPeriodicType wrap = DA_XYPERIODIC;
91: DAStencilType stencil_type = DA_STENCIL_BOX;
92: VecScatter scatter;
94: PetscInitialize(&argc,&argv,(char*)0,help);
95: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
97: /* Read options */
98: PetscOptionsGetInt(PETSC_NULL,"-M",&M,PETSC_NULL);
99: PetscOptionsGetInt(PETSC_NULL,"-N",&N,PETSC_NULL);
100: PetscOptionsGetInt(PETSC_NULL,"-P",&P,PETSC_NULL);
101: PetscOptionsGetInt(PETSC_NULL,"-m",&m,PETSC_NULL);
102: PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
103: PetscOptionsGetInt(PETSC_NULL,"-p",&p,PETSC_NULL);
104: PetscOptionsGetInt(PETSC_NULL,"-s",&s,PETSC_NULL);
105: PetscOptionsHasName(PETSC_NULL,"-star",&flg);
106: if (flg) stencil_type = DA_STENCIL_STAR;
108: /* Create distributed array and get vectors */
109: DACreate3d(PETSC_COMM_WORLD,wrap,stencil_type,M,N,P,m,n,p,1,s,
110: lx,ly,lz,&da);
111: DAView(da,PETSC_VIEWER_DRAW_WORLD);
112: DACreateGlobalVector(da,&global);
113: DACreateLocalVector(da,&local);
115: GenerateSliceScatter(da,&scatter,&vslice);
117: /* Put the value rank+1 into all locations of vslice and transfer back to global vector */
118: value = 1.0 + rank;
119: VecSet(&value,vslice);
120: VecScatterBegin(vslice,global,INSERT_VALUES,SCATTER_REVERSE,scatter);
121: VecScatterEnd(vslice,global,INSERT_VALUES,SCATTER_REVERSE,scatter);
123: VecView(global,PETSC_VIEWER_DRAW_WORLD);
125: VecDestroy(local);
126: VecDestroy(global);
127: DADestroy(da);
128: PetscFinalize();
129: return 0;
130: }