Actual source code: ex39.c

petsc-3.5.4 2015-05-23
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  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:  */

 16: int main(int argc,char **argv)
 17: {
 18:   PetscErrorCode    ierr;
 19:   PetscInt          N = 10,i;
 20:   Vec               X,Y,F,X1,Y1,X2,Y2,F1,F2;
 21:   PetscScalar       value,zero=0.0;
 22:   const PetscScalar *x,*y;
 23:   PetscScalar       *f;

 25:   PetscInitialize(&argc,&argv,(char*)0,help);

 27:   /* create vectors X,Y and F and set values in it*/
 28:   VecCreate(PETSC_COMM_SELF,&X);
 29:   VecSetSizes(X,N,N);
 30:   VecSetFromOptions(X);
 31:   VecDuplicate(X,&Y);
 32:   VecDuplicate(X,&F);
 33:   PetscObjectSetName((PetscObject)F,"F");
 34:   for (i=0; i < N; i++) {
 35:     value = i;
 36:     VecSetValues(X,1,&i,&value,INSERT_VALUES);
 37:     value = 100 + i;
 38:     VecSetValues(Y,1,&i,&value,INSERT_VALUES);
 39:   }
 40:   VecSet(F,zero);

 42:   /* Create subvectors X1,X2,Y1,Y2,F1,F2 */
 43:   VecCreate(PETSC_COMM_SELF,&X1);
 44:   VecSetSizes(X1,N/2,N/2);
 45:   VecSetFromOptions(X1);
 46:   VecDuplicate(X1,&X2);
 47:   VecDuplicate(X1,&Y1);
 48:   VecDuplicate(X1,&Y2);
 49:   VecDuplicate(X1,&F1);
 50:   VecDuplicate(X1,&F2);

 52:   /* Get array pointers for X,Y,F */
 53:   VecGetArrayRead(X,&x);
 54:   VecGetArrayRead(Y,&y);
 55:   VecGetArray(F,&f);
 56:   /* Share X,Y,F array pointers with subvectors */
 57:   VecPlaceArray(X1,x);
 58:   VecPlaceArray(X2,x+N/2);
 59:   VecPlaceArray(Y1,y);
 60:   VecPlaceArray(Y2,y+N/2);
 61:   VecPlaceArray(F1,f);
 62:   VecPlaceArray(F2,f+N/2);

 64:   /* Do subvector addition */
 65:   VecWAXPY(F1,1.0,X1,Y1);
 66:   VecWAXPY(F2,1.0,X2,Y2);

 68:   /* Reset subvectors */
 69:   VecResetArray(X1);
 70:   VecResetArray(X2);
 71:   VecResetArray(Y1);
 72:   VecResetArray(Y2);
 73:   VecResetArray(F1);
 74:   VecResetArray(F2);

 76:   /* Restore X,Y,and F */
 77:   VecRestoreArrayRead(X,&x);
 78:   VecRestoreArrayRead(Y,&y);
 79:   VecRestoreArray(F,&f);

 81:   PetscPrintf(PETSC_COMM_SELF,"F = X + Y\n");
 82:   VecView(F,0);
 83:   /* Destroy vectors */
 84:   VecDestroy(&X);
 85:   VecDestroy(&Y);
 86:   VecDestroy(&F);
 87:   VecDestroy(&X1);
 88:   VecDestroy(&Y1);
 89:   VecDestroy(&F1);
 90:   VecDestroy(&X2);
 91:   VecDestroy(&Y2);
 92:   VecDestroy(&F2);

 94:   PetscFinalize();
 95:   return 0;
 96: }