Hi,

> 'dealii::PETScWrappers::internal::VectorReference::ExcAccessToNonlocalElement'
>
> After some debugging , I got to know that the error is because of the
> following statement:
>
>  fe_v_neighbor.get_function_values(old_f,
>                                   f_values_neighbor);
>
> I comment this out and everything works fine. Here old_f is a variable I
> calculate from advection equation and substitute in the poisson equation.

You are trying to access elements that are not available locally
because the vector memory is distributed between the machines, i.e.
each machine only stores the own elements. You can duplicate the
vector to all machines like this (used at another place in step-17
too):

PETScWrappers::Vector localized_solution (solution);

The vector localized_solution is now available on every machine and
you can use it for get_function_values() etc. Of course you need to
adapt it to your function old_f...

Best,
Timo


-- 
Timo Heister
http://num.math.uni-goettingen.de/~heister
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