Gotm

In the first part of this story, I described ten weeks rewriting a forty-year-old Fortran ocean model in Python — one wrong architectural bet, one painful pivot, and one validation methodology I had to invent because the obvious one was lying to me. It ended at a pre-release: fifteen of the official reference cases passing, the physics validated, and a closing line about what came next. What came next, I wrote, was lakes. Reservoir water quality. The application layer. ...

There is a particular kind of hubris that shows up in engineering projects. It is the moment you look at 87 Fortran files representing forty years of accumulated ocean physics and think: I can do this in Python. Not translate the interface. Not wrap the binary. Rewrite it. Subroutine by subroutine, comment by comment, constant by constant, until what you have is a Python package that produces the same numbers — to a scientifically meaningful degree of precision — as a compiled Fortran model that has been validated against field observations across four decades. ...