MeDiPack: MPI wrapper for Algorithmic Differentiation tools.

MeDiPack (Message Differentiation Package) is a tool for gradient evaluation in computer programs. It supports the features:

• Full forward of the MPI 3.1 specification
• AD handling for nearly all MPI functions
  • This includes:
    • Point to point communication
    • Collective communication
    • Blocking as well as non-blocking variants
  • This excludes (will be handled later):
    • One-Sided communication
    • IO functions

List of supported and unsupported functions

Supported

Most of the MPI standard is covered by the MeDiPack library. The functions that are not supported are mostly very specialized routines. The following general list describes features of MPI that are handled, but makes no claim to be complete:

• Asynchronous communication
• Custom data types
• In place buffers
• Operators
  • Here the interface needed to be extended for AD handling. The default creation of operators will still work but the reduction operations for AD types are handled by performing a gather. Afterwards a local reduce is performed. See the tutorial for further information.

Statistics about the handled functions:

• MPI 1.* 124/129 (96 %)
• MPI 2.* 153/183 (83 %)
• MPI 3.* 70/109 (64 %)
• Total 347/421 (82 %)

Unsupported

Our aim is to support all MPI functions in MeDiPack, therefore most of the functions in this listing will be removed in the next releases. If you require a function that is in the list below please feel free to contact us.

In general the following class of functions are not supported:

• One sided communication
• *w methods
• Fortran conversion functions
• *neighbor* functions
• Handling intercommunicators

The MPI IO functions are just forwarded to there MPI versions. A special handling for the AD types is not implemented.

The missing functions by MPI version:

• MPI 1.0
  • Sendrecv_replace, Pack, Pack_size, Unpack, Reduce_scatter
• MPI 2.0
  • Pack_external, Pack_external_size, Type_create_darray, Unpack_external, Alltoallw, Accumulate, Get, Put, Win_complete, Win_create, Win_fence, Win_free, Win_get_group, Win_lock, Win_post, Win_start, Win_test, Win_wait, Type_create_f90_complex, Type_create_f90_integer, Type_create_f90_real, Type_match_size, Op_c2f, Op_f2c, Request_c2f, Request_f2c, Type_c2f, Type_f2c
• MPI 2.2
  • Reduce_scatter_block
• MPI 3.0
  • Ialltoallw, Ireduce_scatter, Ireduce_scatter_block, Ineighbor_allgather, Ineighbor_allgatherv, Ineighbor_alltoall, Ineighbor_alltoallv, Ineighbor_alltoallw, Neighbor_allgather, Neighbor_allgatherv, Neighbor_alltoall, Neighbor_alltoallv, Neighbor_alltoallw, Compare_and_swap, Fetch_and_op, Get_accumulate, Raccumulate, Rget, Rget_accumulate, Rput, Win_allocate, Win_allocate_shared, Win_attach, Win_create_dynamic, Win_detach, Win_flush, Win_flush_all, Win_flush_local, Win_flush_local_all, Win_get_info, Win_lock_all, Win_set_info, Win_shared_query, Win_sync, Win_unlock_all, Message_c2f, Message_f2c, T_cvar_get_info, T_pvar_get_info

Usage

In order to use MeDiPack in your application the following steps have to be taken:

• Include <medi/medi.hpp> in a global header
• Use the MeDiPack namespace (using namespace medi;)
• Rename all uses of MPI_ to AMPI_
• Include <medi/medi.cpp> file in a translation unit of your program
• Initialize the specific implementation of your AD tool

Hello World Example

The example uses CoDiPack as an AD tool.

#include <medi/medi.hpp>
 
#include <codi.hpp>
#include <codi/tools/mpi/codiMpiTypes.hpp>
 
#include <iostream>
 
using namespace medi;
 
using MpiTypes = codi::CoDiMpiTypes<Real>;
MpiTypes* mpiTypes;
 
int main(int nargs, char** args) {
  AMPI_Init(&nargs, &args);
 
  mpiTypes = new MpiTypes();
 
  int rank;
 
  AMPI_Comm_rank(AMPI_COMM_WORLD, &rank);
 
  codi::RealReverse::Tape& tape = codi::RealReverse::getTape();
  tape.setActive();
 
  codi::RealReverse a = 3.0;
  if( 0 == rank ) {
    tape.registerInput(a);
 
    AMPI_Send(&a, 1, mpiTypes->MPI_TYPE, 1, 42, AMPI_COMM_WORLD);
  } else {
    AMPI_Recv(&a, 1, mpiTypes->MPI_TYPE, 0, 42, AMPI_COMM_WORLD, AMPI_STATUS_IGNORE);
 
    tape.registerOutput(a);
 
    a.setGradient(100.0);
  }
 
  tape.setPassive();
 
  tape.evaluate();
 
  if(0 == rank) {
    std::cout << "Adjoint of 'a' on rank 0 is: " << a.getGradient() << std::endl;
  }
 
  delete mpiTypes;
 
  AMPI_Finalize();
}
 
#if MEDI_HeaderOnly
#include <medi/medi.cpp>
#endif

Please visit the tutorial page for further information.