[petsc-users] Using petsc with an existing domain decomposition.

[Smith, Barry F.]

> On Oct 13, 2019, at 4:24 AM, Pierre Gubernatis via petsc-users <petsc-users at mcs.anl.gov> wrote:
> 
> Hello all,
> 
> It souds that the best way to introduce petsc in a code is not to introduce it, but develop the code over the petsc structure.
> 
> It is probably true but my problem is that my existing code already is equipped with a domain decomposition based on MPI (a typical themal hydraulic with cartesian staggered mesh)
> 
> The user can slice the domain in sub-domains and construct a linear problem by block: each sub-domain assembles its part of the operator and its part of the RHS.

  What do you mean by it's part of the operator? Does it's part of the operator include the coupling with the neighboring subdomains or does it ignore the neighboring subdomains contributions to the operator? How is it storing "its part of the operator"? 

  Barry

I'm not sure what you mean by "assemble a global operator on a given proc"? PETSc never expects the entire global operator to be assembled onto a single processor. It always assumes each process has "a piece" of the entire operator.
> 
> 
> I am wondering what is the best way now to introduce petsc (considering that I don’t want to assemble a global operator on a given proc). Is there an example that would show how to introduce petsc in this situation ?
> 
> Thank you, Pierre