[semi-extrinsic]

As others have pointed out, adding insult to injury, in the Rust version the bulk of the actual calculation is optimized out completely! Adding a print at the end increases the runtime by an order of magnitude.

The Rust community is actively hurt by people doing things like this, no-one takes this type of work seriously.

Edit: please come back when you've replicated and validated at least something like a basic, well-understood finite difference solver of single-phase incompressible Navier-Stokes, and shown that it's either equivalently fast and much easier code, or significantly faster (very unlikely). Do note that a readable Fortran version is going to be ~400 lines, so there's not a terribly large room for improvement. Also, we already have a good language that gives us slower and much easier code, namely Python.