Hessian coloring

[ChrisRackauckas]

For Hessians, one can exploit symmetry in order to further reduce the number of computations that are necessary by finding and using a star coloring.

[gdalle]

SparseMatrixColorings.jl contains symmetric coloring and decompression utilities:

• https://gdalle.github.io/SparseMatrixColorings.jl/stable/api/#ADTypes.symmetric_coloring
• https://gdalle.github.io/SparseMatrixColorings.jl/stable/api/#SparseMatrixColorings.decompress_symmetric!