So, I have one big coupled implicit system.... and then a smaller
implicit system for each variable in the coupled system. I need to
copy the entries from the RHS vector for the big system that
correspond to one variable into the RHS vector for the small system...
Looking around it appears as though Petsc's VecScatter is exactly what
I want.... it takes a list of indices to copy from and to... the
problem I'm having is with the indices.
Obviously the dof_indices (of each system) are both what I want to
copy from and too.... but they are only defined in the context of one
element... I really need to have the global list of all of the
dof_indices for a variable.
I could use the System::local_dof_indices() function I added... which
returns the set of all the local dofs... and then copy it out to a
std::vector and use parallel::allgather() to get the global list of
dofs.
The problem I'm having with all of this is ordering. When i get the
std::set of local dofs... they are going to be sorted. My question
is: is it true that (for instance) the smallest dof_index for a
variable in one system will correspond to the smallest dof index for
that same variable in another system?
Say for instance you have variables u and v.... you create one
implicit system (named "Ben") with _both_ variables in it and 2 more
implicit systems ("John" and "Roy").... where you just add one
variable (either u or v) to each system.
Will the smallest dof_index for u in "Ben" always correspond to the
smallest dof_index for u in "John"? More generally, will the ordering
of dofs correspond between the two systems?
Finally: am I going about this all wrong? Is there a better (easier)
way?
Thanks,
Derek
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