Actual source code: ex3.c
1: /*$Id: ex3.c,v 1.56 2001/08/07 21:29:27 bsmith Exp $*/
3: static char help[] = "Parallel vector layout.nn";
5: /*T
6: Concepts: vectors^setting values
7: Concepts: vectors^local access to
8: Concepts: vectors^drawing vectors;
9: Processors: n
10: T*/
12: /*
13: Include "petscvec.h" so that we can use vectors. Note that this file
14: automatically includes:
15: petsc.h - base PETSc routines petscis.h - index sets
16: petscsys.h - system routines petscviewer.h - viewers
17: */
18: #include petscvec.h
20: int main(int argc,char **argv)
21: {
22: int i,istart,iend,n = 6,ierr,rank,nlocal;
23: PetscScalar v,*array;
24: Vec x;
25: PetscViewer viewer;
27: PetscInitialize(&argc,&argv,(char*)0,help);
28: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
30: PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
31:
32: /*
33: Create a vector, specifying only its global dimension.
34: When using VecCreate(), VecSetSizes() and VecSetFromOptions(),
35: the vector format (currently parallel or sequential) is
36: determined at runtime. Also, the parallel partitioning of
37: the vector is determined by PETSc at runtime.
38: */
39: VecCreate(PETSC_COMM_WORLD,&x);
40: VecSetSizes(x,PETSC_DECIDE,n);
41: VecSetFromOptions(x);
43: /*
44: PETSc parallel vectors are partitioned by
45: contiguous chunks of rows across the processors. Determine
46: which vector are locally owned.
47: */
48: VecGetOwnershipRange(x,&istart,&iend);
50: /* --------------------------------------------------------------------
51: Set the vector elements.
52: - Always specify global locations of vector entries.
53: - Each processor can insert into any location, even ones it does not own
54: - In this case each processor adds values to all the entries,
55: this is not practical, but is merely done as an example
56: */
57: for (i=0; i<n; i++) {
58: v = (PetscReal)(rank*i);
59: VecSetValues(x,1,&i,&v,ADD_VALUES);
60: }
62: /*
63: Assemble vector, using the 2-step process:
64: VecAssemblyBegin(), VecAssemblyEnd()
65: Computations can be done while messages are in transition
66: by placing code between these two statements.
67: */
68: VecAssemblyBegin(x);
69: VecAssemblyEnd(x);
71: /*
72: Open an X-window viewer. Note that we specify the same communicator
73: for the viewer as we used for the distributed vector (PETSC_COMM_WORLD).
74: - Helpful runtime option:
75: -draw_pause <pause> : sets time (in seconds) that the
76: program pauses after PetscDrawPause() has been called
77: (0 is default, -1 implies until user input).
79: */
80: PetscViewerDrawOpen(PETSC_COMM_WORLD,PETSC_NULL,PETSC_NULL,0,0,300,300,&viewer);
81: PetscObjectSetName((PetscObject)viewer,"Line graph Plot");
82: PetscViewerPushFormat(viewer,PETSC_VIEWER_DRAW_LG);
83: /*
84: View the vector
85: */
86: VecView(x,viewer);
88: /* --------------------------------------------------------------------
89: Access the vector values directly. Each processor has access only
90: to its portion of the vector. For default PETSc vectors VecGetArray()
91: does NOT involve a copy
92: */
93: VecGetLocalSize(x,&nlocal);
94: VecGetArray(x,&array);
95: for (i=0; i<nlocal; i++) {
96: array[i] = rank + 1;
97: }
98: VecRestoreArray(x,&array);
100: /*
101: View the vector
102: */
103: VecView(x,viewer);
105: /*
106: Free work space. All PETSc objects should be destroyed when they
107: are no longer needed.
108: */
109: PetscViewerDestroy(viewer);
110: VecDestroy(x);
112: PetscFinalize();
113: return 0;
114: }
115: