Investigate if it is beneficial to use sparse matrix for stoichiometric coeffcients

[jiweiqi]

Arrhenius.jl/src/Solution.jl

Line 56 in 51a2f3d

product_stoich_coeffs = sparse(npz["product_stoich_coeffs"])

Perhaps testing one small mechanism of GRI3.0, and a large one for n-heptane.