What the function of "restore the local form", can i use VecDestroy to free the local form only;
在 2013-08-15 19:13:52，"Jed Brown" <[email protected]> 写道： >丁老师 <[email protected]> writes: > >> I want to know >> 1. What is the relationship between Vhat and LocalVhat. Is the >> LocalVhat a copy of the Vhat plus the Ghost values. I think the >> LocalVhat will consume more memeory than the Vhat, am i right? > >Logically, you should think of them as separate vectors. The global >form contains only the global entries (non-overlapping partition) and >the local form also contains the ghosted entries. If you want to >operate strictly on the global entries, you can access the global form >directly. > >Implementation-wise, the vectors share memory for the global part. This >means that if you build a Krylov space with VecGhost, you have allocated >storage for the ghosted entries for every Krylov vector, even though the >algorithm will never use them. VecGhost is premature "optimization" >("pessimization") in many cases, so consider just using a local work >vector and performing a scatter from global to local. It's probably >much cheaper than you think. > >> 2. can i direct call VecGetArrary to the Vhat if i do not operate on the >> ghost value. >> >> >> >> Vec Vhat; >> Vec LocalVhat; >> double* VhatVec; >> >> >> VecCreateGhost(PETSC_COMM_WORLD,aMesh->Nx*aMesh->Ny/Commsize,PETSC_DECIDE,aMesh->nghosts,&aMesh->ghosts[0],&Vhat); >> >> VecGhostGetLocalForm(Vhat,&LocalVhat); > >Update, _then_ get the local form. Remember to restore the local form >when you are done with it. > >> VecGhostUpdateBegin(Vhat,INSERT_VALUES,SCATTER_FORWARD); >> VecGhostUpdateEnd(Vhat,INSERT_VALUES,SCATTER_FORWARD);
