Adding std::ops::Inv

libs
13

Rust isn't really a mathematical language like Julia is. num is a library of mathematical traits.

But here's the real sticker for making this a std trait:

  • What types (other than library Matrix types) should implement Inv?
    • What std types?
      • Note that many matrix-providing libraries like numpy implement matrix inversion copyless by dynamically switching between a row-major and a column-major interpretation of the data. [[T; N]; M] would be expensive to reorganize to invert to [[T; M]; N].
      • Plus most users would prefer Matrix<M, N> to [[T; M], N] anyway, for indexing [(row, col)] rather than [col][row].
  • What functionality can meaningfully be input parametric over Inv types (probably with other bounds as well)?
    • What std functionality?

If the trait exists solely just to collect the same functionality under one name, but is not really meaningful as input parametricity, it doesn't really deserve (/need) to be a trait.

TL;DR I don't see any benefit of "matrix inversion" being a standard trait if there isn't even a matrix type in std. And [[T; N]; M] isn't a matrix, it's an array of arrays, which is often used to implement a matrix. And if nothing other than matrices can be inverted, then it would be better as a MatrixOps trait, imho, and that would live in the numpy equivalent for Rust (currently, ~num/nalgebra/ndarray, will definitely shift some when const generics stabilize.).

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