parallel_histogram.C

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


// C++ includes
#include <algorithm>  // is_sorted, lower_bound

// Local includes
#include "libmesh/parallel_histogram.h"
#include "libmesh/parallel.h"
#include "libmesh/parallel_conversion_utils.h"
#include "libmesh/parallel_hilbert.h"

namespace libMesh
{



namespace Parallel {
template <typename KeyType, typename IdxType>
Histogram<KeyType,IdxType>::Histogram (const Parallel::Communicator & comm_in,
                                       const std::vector<KeyType> & d) :
  ParallelObject(comm_in),
  data(d)
{
  libmesh_assert (std::is_sorted (data.begin(), data.end()));
}



template <typename KeyType, typename IdxType>
void Histogram<KeyType,IdxType>::make_histogram (const IdxType nbins,
                                                 KeyType max,
                                                 KeyType min)
{
  libmesh_assert_less (min, max);

  // The width of each bin.  Store this as a floating point value
  double bin_width = (Parallel::Utils::to_double(max)-
                      Parallel::Utils::to_double(min))/static_cast<double>(nbins);


  // The idea for 4 bins of size d is this:
  //
  //  0          1          2           3          4
  //  |----------|----------|-----------|----------|
  // min   0   min+d  1   min+2d  2  min+3d   3   max



  // Set the iterators corresponding to the boundaries
  // as defined above.  This takes nbins * O(log N) time.
  bin_bounds.resize (nbins+1);
  bin_iters.resize  (nbins+1, data.begin());

  // Set the minimum bin boundary iterator
  bin_iters[0]  = data.begin();
  bin_bounds[0] = Parallel::Utils::to_double(min);

  // Set the internal bin boundary iterators
  for (IdxType b=1; b<nbins; ++b)
    {
      bin_bounds[b] = Parallel::Utils::to_double(min) + bin_width * b;

      bin_iters[b] =
        std::lower_bound (bin_iters[b-1], data.end(),
                          Parallel::Utils::Convert<KeyType>::to_key_type(bin_bounds[b]));
    }

  bin_iters[nbins]  = data.end();
  bin_bounds[nbins] = Parallel::Utils::to_double(max);
}



template <typename KeyType, typename IdxType>
void Histogram<KeyType,IdxType>::build_histogram ()
{
  // Build a local histogram
  std::vector<IdxType> local_hist (this->n_bins());

  for (auto b : index_range(local_hist))
    local_hist[b] = this->local_bin_size(b);

  // Add all the local histograms to get the global histogram
  hist = local_hist;
  this->comm().sum(hist);

  // All done!
}

}


// Explicitly instantiate for int, double
template class LIBMESH_EXPORT Parallel::Histogram<int,    unsigned int>;
template class LIBMESH_EXPORT Parallel::Histogram<double, unsigned int>;
#ifdef LIBMESH_HAVE_LIBHILBERT
template class LIBMESH_EXPORT Parallel::Histogram<Parallel::DofObjectKey, unsigned int>;
#endif

} // namespace libMesh