message: use unordered_map instead of map
diff: #include "adios2/common/ADIOSTypes.h"
  #include "adios2/core/IO.h"
  #include "nlohmann/json.hpp"
  -#include <map>
  #include <mpi.h>
  +#include <unordered_map>
  #include <vector>
  namespace adios2
  @@ -40,7 +40,7 @@ struct BlockInfo
  };
  using BlockVec = std::vector<BlockInfo>;
  using BlockVecVec = std::vector<BlockVec>;
  -using RankPosMap = std::map<int, std::pair<size_t, size_t>>;
  +using RankPosMap = std::unordered_map<int, std::pair<size_t, size_t>>;
  using MpiInfo = std::vector<std::vector<int>>;
  void PrintDims(const Dims &dims, const std::string &label = std::string());
  