// a vector that indicates which subdomain
// each cell belongs to. This will make for
// some nice pictures of partitioned domains.
+ //
+ // In practice, the present implementation of
+ // the output function is a major bottleneck
+ // of this program, since generating
+ // graphical output is expensive and doing so
+ // only on one process does, of course, not
+ // scale if we significantly increase the
+ // number of processes. In effect, this
+ // function will consume most of the run-time
+ // if you go to very large numbers of
+ // unknowns and processes, and real
+ // applications should limit the number of
+ // times they generate output through this
+ // function.
+ //
+ // The solution to this is to have each
+ // process generate output data only for it's
+ // own local cells, and write them to
+ // separate files, one file per process. This
+ // would distribute the work of generating
+ // the output to all processes equally. In a
+ // second step, separate from running this
+ // program, we would then take all the output
+ // files for a given cycle and merge these
+ // parts into one single output file. This
+ // has to be done sequentially, but can be
+ // done on a different machine, and should be
+ // relatively cheap. However, the necessary
+ // functionality for this is not yet
+ // implemented in the library, and since we
+ // are too close to the next release, we do
+ // not want to do such major destabilizing
+ // changes any more. It will be fixed in
+ // later releases of the library and this
+ // example program, though.
template <int dim>
void ElasticProblem<dim>::output_results (const unsigned int cycle) const
{
// distributed vector, which is in fact
// simple:
const PETScWrappers::Vector localized_solution (solution);
- // The thing to realize, however, is that
+ // The thing to notice, however, is that
// we do this localization operation on all
// processes, not only the one that
// actually needs the data. This can't be
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