message: Partial progress toward trivial multidomain.
diff: #include <string>
  #include <limits>
  #include <map>
  +#include <vector>
  #include <cmath>
  namespace quest = axom::quest;
  @@ -198,7 +199,8 @@ public:
  explicit BlueprintParticleMesh(sidre::Group* group = nullptr,
  const std::string& coordset = "coords",
  const std::string& topology = "mesh")
  - : m_group(group)
  + : m_group(group),
  + m_domainGroups()
  {
  MPI_Comm_rank(MPI_COMM_WORLD, &m_rank);
  MPI_Comm_size(MPI_COMM_WORLD, &m_nranks);
  @@ -426,6 +428,9 @@ private:
  void createBlueprintStubs(const std::string& coords, const std::string& topo)
  {
  SLIC_ASSERT(m_group != nullptr);
  + SLIC_ASSERT(m_domainGroups.empty());
  + m_domainGroups.resize(1, nullptr);
  + // BTNG TODO: put child domain group in m_group and other groups under the child group.
  m_coordsGroup = m_group->createGroup("coordsets")->createGroup(coords);
  m_coordsGroup->createViewString("type", "explicit");
  @@ -444,6 +449,8 @@ private:
  private:
  /// Parent group for the entire mesh
  sidre::Group* m_group;
  + /// Group for each domain in multidomain mesh
  + std::vector<sidre::Group*> m_domainGroups;
  sidre::Group* m_coordsGroup;
  sidre::Group* m_topoGroup;
  