Actual source code: ex2.c
2: static char help[] = "Builds a parallel vector with 1 component on the first processor, 2 on the second, etc.\n\
3: Then each processor adds one to all elements except the last rank.\n\n";
5: /*T
6: Concepts: vectors^assembling vectors;
7: Processors: n
8: T*/
10: /*
11: Include "petscvec.h" so that we can use vectors. Note that this file
12: automatically includes:
13: petscsys.h - base PETSc routines petscis.h - index sets
14: petscviewer.h - viewers
15: */
16: #include <petscvec.h>
18: int main(int argc,char **argv)
19: {
20: PetscMPIInt rank;
21: PetscInt i,N;
22: PetscScalar one = 1.0;
23: Vec x;
25: PetscInitialize(&argc,&argv,(char*)0,help);
26: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
28: /*
29: Create a parallel vector.
30: - In this case, we specify the size of each processor's local
31: portion, and PETSc computes the global size. Alternatively,
32: if we pass the global size and use PETSC_DECIDE for the
33: local size PETSc will choose a reasonable partition trying
34: to put nearly an equal number of elements on each processor.
35: */
36: VecCreate(PETSC_COMM_WORLD,&x);
37: VecSetSizes(x,rank+1,PETSC_DECIDE);
38: VecSetFromOptions(x);
39: VecGetSize(x,&N);
40: VecSet(x,one);
42: /*
43: Set the vector elements.
44: - Always specify global locations of vector entries.
45: - Each processor can contribute any vector entries,
46: regardless of which processor "owns" them; any nonlocal
47: contributions will be transferred to the appropriate processor
48: during the assembly process.
49: - In this example, the flag ADD_VALUES indicates that all
50: contributions will be added together.
51: */
52: for (i=0; i<N-rank; i++) {
53: VecSetValues(x,1,&i,&one,ADD_VALUES);
54: }
56: /*
57: Assemble vector, using the 2-step process:
58: VecAssemblyBegin(), VecAssemblyEnd()
59: Computations can be done while messages are in transition
60: by placing code between these two statements.
61: */
62: VecAssemblyBegin(x);
63: VecAssemblyEnd(x);
65: /*
66: View the vector; then destroy it.
67: */
68: VecView(x,PETSC_VIEWER_STDOUT_WORLD);
69: VecDestroy(&x);
71: PetscFinalize();
72: return 0;
73: }
75: /*TEST
77: test:
78: nsize: 2
80: TEST*/