Actual source code: ex39.c
petsc-3.12.1 2019-10-22
2: static char help[] = "This example is intended for showing how subvectors can\n\
3: share the pointer with the main vector using VecGetArray()\n\
4: and VecPlaceArray() routines so that vector operations done\n\
5: on the subvectors automatically modify the values in the main vector.\n\n";
7: #include <petscvec.h>
9: /* This example shares the array pointers of vectors X,Y,and F with subvectors
10: X1,X2,Y1,Y2,F1,F2 and does vector addition on the subvectors F1 = X1 + Y1, F2 = X2 + Y2 so
11: that F gets updated as a result of sharing the pointers.
12: */
14: int main(int argc,char **argv)
15: {
16: PetscErrorCode ierr;
17: PetscInt N = 10,i;
18: Vec X,Y,F,X1,Y1,X2,Y2,F1,F2;
19: PetscScalar value,zero=0.0;
20: const PetscScalar *x,*y;
21: PetscScalar *f;
23: PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
25: /* create vectors X,Y and F and set values in it*/
26: VecCreate(PETSC_COMM_SELF,&X);
27: VecSetSizes(X,N,N);
28: VecSetFromOptions(X);
29: VecDuplicate(X,&Y);
30: VecDuplicate(X,&F);
31: PetscObjectSetName((PetscObject)F,"F");
32: for (i=0; i < N; i++) {
33: value = i;
34: VecSetValues(X,1,&i,&value,INSERT_VALUES);
35: value = 100 + i;
36: VecSetValues(Y,1,&i,&value,INSERT_VALUES);
37: }
38: VecSet(F,zero);
40: /* Create subvectors X1,X2,Y1,Y2,F1,F2 */
41: VecCreate(PETSC_COMM_SELF,&X1);
42: VecSetSizes(X1,N/2,N/2);
43: VecSetFromOptions(X1);
44: VecDuplicate(X1,&X2);
45: VecDuplicate(X1,&Y1);
46: VecDuplicate(X1,&Y2);
47: VecDuplicate(X1,&F1);
48: VecDuplicate(X1,&F2);
50: /* Get array pointers for X,Y,F */
51: VecGetArrayRead(X,&x);
52: VecGetArrayRead(Y,&y);
53: VecGetArray(F,&f);
54: /* Share X,Y,F array pointers with subvectors */
55: VecPlaceArray(X1,x);
56: VecPlaceArray(X2,x+N/2);
57: VecPlaceArray(Y1,y);
58: VecPlaceArray(Y2,y+N/2);
59: VecPlaceArray(F1,f);
60: VecPlaceArray(F2,f+N/2);
62: /* Do subvector addition */
63: VecWAXPY(F1,1.0,X1,Y1);
64: VecWAXPY(F2,1.0,X2,Y2);
66: /* Reset subvectors */
67: VecResetArray(X1);
68: VecResetArray(X2);
69: VecResetArray(Y1);
70: VecResetArray(Y2);
71: VecResetArray(F1);
72: VecResetArray(F2);
74: /* Restore X,Y,and F */
75: VecRestoreArrayRead(X,&x);
76: VecRestoreArrayRead(Y,&y);
77: VecRestoreArray(F,&f);
79: PetscPrintf(PETSC_COMM_SELF,"F = X + Y\n");
80: VecView(F,0);
81: /* Destroy vectors */
82: VecDestroy(&X);
83: VecDestroy(&Y);
84: VecDestroy(&F);
85: VecDestroy(&X1);
86: VecDestroy(&Y1);
87: VecDestroy(&F1);
88: VecDestroy(&X2);
89: VecDestroy(&Y2);
90: VecDestroy(&F2);
92: PetscFinalize();
93: return ierr;
94: }