Actual source code: ex2.c
petsc-3.10.5 2019-03-28
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: {
21: PetscMPIInt rank;
22: PetscInt i,N;
23: PetscScalar one = 1.0;
24: Vec x;
26: PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
27: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
29: /*
30: Create a parallel vector.
31: - In this case, we specify the size of each processor's local
32: portion, and PETSc computes the global size. Alternatively,
33: if we pass the global size and use PETSC_DECIDE for the
34: local size PETSc will choose a reasonable partition trying
35: to put nearly an equal number of elements on each processor.
36: */
37: VecCreate(PETSC_COMM_WORLD,&x);
38: VecSetSizes(x,rank+1,PETSC_DECIDE);
39: VecSetFromOptions(x);
40: VecGetSize(x,&N);
41: VecSet(x,one);
43: /*
44: Set the vector elements.
45: - Always specify global locations of vector entries.
46: - Each processor can contribute any vector entries,
47: regardless of which processor "owns" them; any nonlocal
48: contributions will be transferred to the appropriate processor
49: during the assembly process.
50: - In this example, the flag ADD_VALUES indicates that all
51: contributions will be added together.
52: */
53: for (i=0; i<N-rank; i++) {
54: VecSetValues(x,1,&i,&one,ADD_VALUES);
55: }
57: /*
58: Assemble vector, using the 2-step process:
59: VecAssemblyBegin(), VecAssemblyEnd()
60: Computations can be done while messages are in transition
61: by placing code between these two statements.
62: */
63: VecAssemblyBegin(x);
64: VecAssemblyEnd(x);
66: /*
67: View the vector; then destroy it.
68: */
69: VecView(x,PETSC_VIEWER_STDOUT_WORLD);
70: VecDestroy(&x);
72: PetscFinalize();
73: return ierr;
74: }
76: /*TEST
78: test:
79: nsize: 2
81: TEST*/