In-place versions for matrix operations when using mutable static arrays

[aplesner]

There are currently no in-place implementations for lu factorization and ldiv when using mutable matrices/vectors (MMatrix and MVector). This currently causes errors when using a stiff ODE solvers with the state being an MVector.

This may be related to issue #1031.

[j-fu]

I am missing this as well so I am dabbling with my own codes on need.

That code also should work with StrideArrays etc. Being non-allocating IMHO is a must, so there should be a e.g. LU factorization where one can pass ipiv.

BTW, in 1.9

ldiv!(b, RecursiveFactorization.lu!(A, ipiv, Val(true), Val(false)), b)

works.