Trouble with DA, multiple degrees of freedom

Pearl Flath pflath at
Tue Feb 5 13:50:51 CST 2008

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.
Pearl Flath
ICES, UT Austin

  DACreateGlobalVector(daV, &vel);

  // Set the velocity file to read from
  PetscTruth flg ;
  PetscViewer view_u;
  char velocityfile[1024] ;

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