On 3/1/19 8:54 PM, Jean Ragusa wrote: > > I have a solution vector with locally owned and locally relevant dofs. I want > to compute its L2-norm. Using the l2_norm() on it caused a Trilinos error (I > was going to compute the squared of the L2 norm, then do an MPI Allreduce on > the resulting values). > > So, I decided to code it "by hand" as follows: > > double norm_squared = 0.; > const unsigned int start_ = (dist_solution.local_range().first), end_ = > (dist_solution.local_range().second); > > for (unsigned int i = start_; i < end_; ++i) > norm_squared += std::pow(dist_solution(i),2); > > double norm_global =0.; > MPI_Allreduce(&norm_squared, &norm_global, 1, MPI_DOUBLE, MPI_SUM, > mpi_communicator); > norm_global = std::sqrt(norm_global); > > > Even though this works, I was wondering if there is a better way to do this?
Yes! Create a completely distributed vector, copy your ghosted vector into it, and then compute the l2 norm of that completely distributed vector. That's going to cost a bit of communication, but I suspect you're not doing it often enough to actually feel the difference :-) Cheers W. -- ------------------------------------------------------------------------ Wolfgang Bangerth email: [email protected] www: http://www.math.colostate.edu/~bangerth/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
