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Section: New Results

AD-adjoints of MPI-parallel codes

Participants : Laurent Hascoët, Ala Taftaf, Georgios Ntanakas [Rolls-Royce, Dahlewitz, Germany] , Sri Hari Krishna Narayanan [Argonne National Lab. (Illinois, USA)] .

We have a long-standing collaboration with Argonne National Lab on the question of adjoint AD of message-passing parallel codes. We continued joint development of the Adjoinable-MPI library (AMPI) that provides efficient tangent and adjoint AD for MPI-parallel codes, independently of the AD tool used (now AdolC, dco, OpenAD, Tapenade).

Ala Taftaf considers the question of checkpointing applied to the AD-adjoint of an MPI-parallel code. Checkpointing is a memory/runtime tradeoff which is essential for adjoint AD of large codes, in particular parallel codes. However, for MPI codes this question has always been addressed by ad-hoc hand manipulations of the differentiated code, and with no formal assurance of correctness. Ala Taftaf studies these past experiments and proposes more general strategies. Ala Taftaf presented her results [20], [23] at the Eccomas 2016 conference (Crete) in June and at the NOED 2016 conference (Munich) in july [22].

During his secondment with our team, PhD student Georgios Ntanakas from Rolls-Royce studied possible extension of Tapenade to handle the parallel constructs in Rolls-Royce's “Hydra” code, which rely on a special parallel library named “OPlus”.