LEWG VS mdspan

https://github.com/cplusplus/LEWG/wiki/2021-Telecons I want to learn some proposal and I found there're some telecons, but when I clicked the URL, it showed that I need to be invited...But how?

This post only covers what is, and could have been, for consideration in the next two months of time before C++23 is considered feature complete. It doesn't cover proposals that where already discussed. If you look at the linked telecons schedule (https://github.com/cplusplus/LEWG/wiki/2021-Telecons) you'll see that constexpr math was discussed in June. You would need to further search in the papers status list (https://github.com/cplusplus/papers/issues) to see where each one is at in the road to C++23.

On 2021-05-11, hopefully. I haven't gotten confirmation from the authors yet.

Why not use https://github.com/kokkos/mdspan though ?

It can be the base of whatever *you* write via bindings generators like pybind11. In that sense, the answer to your question is "however you like". For actual simulation code, you'll see a lot more legacy Fortran and C. That said, with things like mdspan maybe being standardized (proposal), efforts towards a standard linear algebra library, and the existence of ubiquitous HPC frameworks already having been written in C++, I would say it's only a matter of time before C++ accounts for an even bigger share of all HPC code.

I'm aware of only two relevant projects myself, I don't know much, came to reddit kind of by chance. One of the multi-dimensional array libraries proposed for potential standardisation, and a gnu machine learning library that was discontinued which could be worked off of. There's probably a lot more out there, but don't get distracted from making something awesome :)

As u/IyeOnline already made the important points about VLAs and std::vector, I would just add that you may find std::mdspan to be a helpful data structure. You can allocate 1d memory and give it a 2d shape of k with nice 2d indexing, eg auto& elem = mymdspan(row, col);.

Kokkos mdspan

The good thing here is that it heavily relies on mdpsan that is a multidimensional view that handle shape and strides. And kokkos provide a C++14 compatible implementation with a complete CUDA support.