Matrix implemented as a graph, specially for the use case when it should be auto expanding at custom rate, specially in simulations. It is a header-only library, and utilises graphs internally. Relies heavily on templates, though if you use it the wrong way, it will be a one line compile error instead of deep errors into standard library code, in most cases.

Usage is pretty simple, the docs are brief and to the point, get started with auto expansion, in just 2 lines, stable API as tested with unit tests, put in the repo itself. Though `special usecase` is auto expanding, even if you just need a 3D matrix, there won't be overhead for what you aren't using, can be accessed just like a 3D vector, arr[i][j][k] === arr[{i, j, k}]