Differentiable Fortran with LFortran and Enzyme

Differentiable Fortran with LFortran and Enzyme(docs.pasteurlabs.ai)

31 points by dionhaefner 3 hours ago | 8 comments

Author here — I work on Tesseract at Pasteur Labs, and I wrote this up because the "what if this was possible" was bugging me for way too long :)

I was surprised by how well this worked, the LFortran + Enzyme stack seems to be a very clean way to get gradients through Fortran code via LLVM IR transformations. Pretty cool to see a 220-line Fortran heat solver turn into ~6,900-line reverse pass automatically if I dare say so.

Would be awesome to see this applied to a real scientific codebase, and I hope that the demo is enough to convince people that it’s worth trying.

srean 1 hour ago | |

Very interesting. Does LFortran have the same internal array layout as the standard C runtime ?

A shared layout and a shared calling convention would be very nice.

Sorry about my naive question. Haven't touched Fortran directly in three decades I think.

EDIT: thanks for your reply. For some reason it has been flagged dead. So am responding here. You can mail dang hn at ycombinator dot co m about the flagging. He is very nice.

kmaitreys 3 minutes ago | | |

I would also like to know this. Fortran itself is column-major, so I would guess the internal layout isn't same for multi-dimensional arrays when compared to row-major C? I'm not sure how LFortran represents arrays internally though.

wombatpm 1 hour ago | | |

Lots of scientific code in Fortran has sparse arrays, so a NxN array that only has values on 5 diagonals will store that as 5xN array to save memory allowing you to run a larger problem.

tanderson92 23 minutes ago | |

When you say you 'wrote this up', you mean you had an AI write (at least) chunks of it.

dionhaefner 15 minutes ago | | |

Indeed, just like I let my compiler write (at least) chunks of my AD logic. Not great when the tool becomes a leaky abstraction, but overall net positive don't you think?