New optimized variable-coefficient second-derivative operators of Stierström, Almquist, Mattsson

[ranocha]

Stiernström, Vidar and Almquist, Martin and Mattsson, Ken Roger, Boundary-Optimized Summation-by-Parts Operators for Finite Difference Approximations of Second Derivatives with Variable Coefficients. Available at SSRN: https://ssrn.com/abstract=4353569 or http://dx.doi.org/10.2139/ssrn.4353569

[ranocha]

Coefficients available at https://github.com/VidarStiernstrom/bopt_sbp_ops