Zoltan2_AlgBlockMapping.hpp

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// @HEADER
// *****************************************************************************
//   Zoltan2: A package of combinatorial algorithms for scientific computing
//
// Copyright 2012 NTESS and the Zoltan2 contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER
 
#ifndef _ZOLTAN2_ALGBLOCKMAPPING_HPP_
#define _ZOLTAN2_ALGBLOCKMAPPING_HPP_
 
#include <Zoltan2_Standards.hpp>
#include <Zoltan2_Algorithm.hpp>
#include <Zoltan2_PartitioningSolution.hpp>
#include <Zoltan2_Util.hpp>
#include <Tpetra_Map.hpp>
#include <set>
#include <cmath>
 
//         are contiguously numbered from 0 to nParts-1
//         This use case is common; because it requires no explicit storage
//         of the parts to ranks,
//         we separate it from methods that do need extra storage.
 
namespace Zoltan2 {
 
template <typename Adapter, typename MachineRep>
class AlgBlockMapping : public Algorithm<Adapter>
{
 
private:
 
  typedef typename Adapter::lno_t lno_t;
  typedef typename Adapter::gno_t gno_t;
  typedef typename Adapter::scalar_t scalar_t;
  typedef typename Adapter::part_t part_t;
  typedef typename Adapter::user_t user_t;
  typedef typename Adapter::userCoord_t userCoord_t;
 
public:
 
  AlgBlockMapping(
    const Teuchos::RCP <const Teuchos::Comm<int> > &comm_,
    const Teuchos::RCP <const MachineRep> &machine_,
    const Teuchos::RCP <const Adapter> &adapter_,
    const Teuchos::RCP <const Zoltan2::PartitioningSolution<Adapter> > &psoln_,
    const Teuchos::RCP <const Environment> &envConst):
    nRanks(comm_->getSize()), myRank(comm_->getRank()),
    nMyParts(0), myParts(Teuchos::null)
  { 
    // Get set of parts from partitioning solution or adapter, if provided
    // Otherwise, we'll assume set of parts == set of ranks
    const part_t *partList;
    if (psoln_ != Teuchos::null) {
      partList = psoln_->getPartListView();
    }
    else {
      adapter_->getPartsView(partList);
    }
 
    // Compute maxPart, nParts
 
    part_t minPart, maxPart;
 
    if (partList == NULL) {
      // Parts for IDs are the same as ranks
      nParts = nRanks;
      maxPart = nRanks-1;
      minPart = 0;
    }
    else {
      // Parts were provided by partitioning solution or input adapter
 
      // Find unique parts on this rank, 
      // as Tpetra::Map does not like duplicate GIDs within a rank
 
      size_t nLocal = adapter_->getLocalNumIDs();
 
      // Ideally, we'd use part_t as global ID in the map, but that won't
      // work if Tpetra is compiled without global ID = int.
      //    typedef part_t use_this_gno_t;
      // We'll use Tpetra's default instead
      typedef Tpetra::Map<>::global_ordinal_type use_this_gno_t;
 
      std::set<use_this_gno_t> unique;
      for (size_t i = 0; i < nLocal; i++)
        unique.insert(partList[i]);
 
      size_t nUnique = unique.size();
      Array<use_this_gno_t> uniquePartList(nUnique);
      size_t k = 0;
      for (typename std::set<use_this_gno_t>::iterator it = unique.begin();
           it != unique.end(); it++)
        uniquePartList[k++] = *it;
        
      // Use Tpetra::Map to find the max, min, total part.
 
      global_size_t nGlobalElts = 
                    Teuchos::OrdinalTraits<Tpetra::global_size_t>::invalid();
      Tpetra::Map<lno_t, use_this_gno_t> tmap(nGlobalElts, uniquePartList(),
                                              0, comm_);
 
      nParts = Teuchos::as<part_t>(tmap.getGlobalNumElements());
      minPart = tmap.getMinAllGlobalIndex();
      maxPart = tmap.getMaxAllGlobalIndex();
    }
 
    // Determine number of unique parts, as well as min and max part
    // Can probably use a Tpetra Map.
 
    if ((minPart != 0) || (maxPart != nParts-1)) {
      // Cannot use this mapping method
      throw std::runtime_error("Cannot use mapping_algorithm = contiguous "
                               "unless parts are numbered from 0 to nParts-1");
    }
 
    sharedConstructor();
  }
 
  //         submethod of the default
  //         Assume that calling method has already confirmed assumptions
  //         about part numbering.
  AlgBlockMapping(
    const Teuchos::RCP <const Teuchos::Comm<int> > comm_,
    const part_t nparts) :
    nRanks(comm_->getSize()),
    nParts(nparts),  
    myRank(comm_->getRank()),
    nMyParts(0),
    myParts(Teuchos::null)
  {
    sharedConstructor();
  }
 
  void sharedConstructor()
  {
    nParts_Div_nRanks = nParts / nRanks;
    nParts_Mod_nRanks = nParts % nRanks;
    nMyParts = nParts_Div_nRanks + (myRank < nParts_Mod_nRanks);
  }
 
  void map(const Teuchos::RCP<MappingSolution<Adapter> > &msoln) {
    // Mapping is computed implicitly; 
    // nothing to do here since we implement 
    // getRankForPart and getMyPartsView.
  }
 
  int getRankForPart(part_t p) {
    if (p < 0 || p >= nParts)
      throw std::runtime_error("Invalid part in getRankForPart");
 
    int tmp = p / nParts_Div_nRanks;
    while (firstPart(tmp) > p) tmp--;
    while (firstPart(tmp+1) < p) tmp++;
    return tmp;
  }
 
  void getMyPartsView(part_t &numParts, part_t *&parts)
  {
    // Will need to construct the arrays if this function is called.
    // Will not work if this is a const method.
    numParts = nMyParts;
    if (nMyParts) {
      if (myParts == Teuchos::null) {
        myParts = arcp(new part_t[nMyParts], 0, nMyParts, true);
        for (part_t i = 0; i < nMyParts; i++)
          myParts[i] = firstPart(myRank) + i;
      }
      parts = myParts.getRawPtr();
    }
    else
      parts = NULL;
  }
 
private:
 
  inline part_t firstPart(int rank) {
    // For contiguous part assignments, the first part assigned to rank
    return (rank * nParts_Div_nRanks + std::min(rank, nParts_Mod_nRanks));
  }
 
  const int nRanks;            // Global number of ranks
  part_t nParts;               // Global number of parts
  part_t nParts_Div_nRanks;    // (nParts/nRanks) precomputed for frequent use
  part_t nParts_Mod_nRanks;    // (nParts%nRanks) precomputed for frequent use
 
  const int myRank;            // Local rank
  part_t nMyParts;       // Local number of parts
  ArrayRCP<part_t> myParts;  // Array of my parts; created only if 
                                   // getMyPartsView is called.
}; 
 
 
} // namespace Zoltan2
 
#endif