18335 VS Fortran-code-on-GitHub

I would say Fortran is a pretty great language for teaching beginners in numerical analysis courses. The only issue I have with it is that, similar to using C+MPI (which is what I first learned with, well after a bit of Java), the students don't tend to learn how to go "higher level". You teach them how to write a three loop matrix-matrix multiplication, but the next thing you should teach is how to use higher level BLAS tools and why that will outperform the 3-loop form. But Fortran then becomes very cumbersome (`dgemm` etc.) so students continue to write simple loops and simple algorithms where they shouldn't. A first numerical analysis course should teach simple algorithms AND why the simple algorithms are not good, but a lot of instructors and tools fail to emphasize the second part of that statement.

On the other hand, the performance + high level nature of Julia makes it a rather excellent tool for this. In MIT graduate course 18.337 Parallel Computing and Scientific Machine Learning (https://github.com/mitmath/18337) we do precisely that, starting with direct optimization of loops, then moving to linear algebra, ODE solving, and implementing automatic differentiation. I don't think anyone would want to give a homework assignment to implement AD in Fortran, but in Julia you can do that as something shortly after looking at loop performance and SIMD, and that's really something special. Steven Johnson's 18.335 graduate course in Numerical Analysis (https://github.com/mitmath/18335) showcases some similar niceties. I really like this demonstration where it starts from scratch with the 3 loops and shows how SIMD and cache-oblivious algorithms build towards BLAS performance, and why most users should ultimately not be writing such loops (https://nbviewer.org/github/mitmath/18335/blob/master/notes/...) and should instead use the built-in `mul!` in most scenarios. There's very few languages where such "start to finish" demonstrations can really be showcased in a nice clear fashion.

The hints in place ("there is more infrastructure already available outside Fortran, consider using them instead"). Beliavsky's compilation Fortran code on GitHub with its section about neural networks and machine learning still may be worth a visit e.g. how let Fortran reach out for the implementations in other languages.

There is an interesting directories compiled about projects around Fortran, Fortran code on GitHub. Though artificial intelligence does not appear by name, section Neural networks and Machine Learning may provide an entry.

My list of Fortran codes on GitHub has a section Containers and Generic Programming with some of the data structures you mention.

There's modern stuff being written in astro(nomy/physics) (I can attest to some of the codebases listed in https://github.com/Beliavsky/Fortran-code-on-GitHub#astrophy... being modern, at least in terms of development), but I'd say C++ likely does have the upper hand for newer codebases (unless things have changed dramatically last time I looked, algorithms that don't nicely align with nd-arrays are still painful in Fortran).

I've also heard rumours of Julia and even Rust being used (the latter because of the ability to reuse libraries in the browser e.g. for visualisation), but the writers of these codebases (and the Fortran/C/C++/Java) are unusual—Python and R (and for some holdouts, IDL) are what are most people write in (even if those languages call something else).

"QuantEcon:Open source code for economic modeling" https://quantecon.org/ has Python and Julia versions. The Federal Reserve uses Julia in its macroeconomic models: https://frbny-dsge.github.io/DSGE.jl/latest/ . Some economists use Fortran (which is much modernized since FORTRAN 77), and there is a 2018 book Introduction to Computational Economics using Fortran https://www.ce-fortran.com/ . Some Fortran codes in economics, statistics, and time series analysis are listed at https://github.com/Beliavsky/Fortran-code-on-GitHub .

At the "Fortran Code on GitHub" repo https://github.com/Beliavsky/Fortran-code-on-GitHub there are many codes listed in the "Climate and Weather" and "Earth Science" sections.

Fortran 77 and later versions (most recently Fortran 2018) have strings. There is the limitation that the elements of an array of strings must have equal length, so that ["boy","girl"] is invalid but ["boy ","girl"] is. Libraries for manipulating strings in Fortran are listed at https://github.com/Beliavsky/Fortran-code-on-GitHub#strings .