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Re: Trouble with DA, multiple degrees of freedom


  VecStrideScale() is the easiest way to do this.

   Barry

On Feb 5, 2008, at 1:50 PM, Pearl Flath wrote:

Dear All,
I have a code where the velocity (three components) and pressure are all stored in a distributed array with 4 degrees of freedom per node. I'd like to take one component of the velocity and multiply it by -1, but I am having trouble figuring out how to access that. I believe it must involve DAVecGetArrayDOF or DAVecGetArray, but I haven't managed to get either to work. I've attached a code fragment where it loads the velocity. Could someone suggest how to do this or point me to where I can find additional discussion of this? I've read the users manual on DA already.
Sincerely,
Pearl Flath
ICES, UT Austin
---------------------------------
DACreate3d(PETSC_COMM_WORLD,DA_NONPERIODIC,DA_STENCIL_BOX,m,n,p,
PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,
4,1,PETSC_NULL,PETSC_NULL,PETSC_NULL,&daV);

  DACreateGlobalVector(daV, &vel);

  // Set the velocity file to read from
  PetscTruth flg ;
  PetscViewer view_u;
  char velocityfile[1024] ;
  PetscOptionsGetString(0,"-velocityfile",velocityfile,1023,&flg);

  PetscViewerBinaryOpen(PETSC_COMM_WORLD, velocityfile,
                        FILE_MODE_READ, &view_u);
  VecLoadIntoVector(view_u, vel);
  PetscViewerDestroy(view_u);