Cubics and quartics

[ivan-pi]

For cubics and quartics, a Fortran solver was published recently in ACM TOMS:

Flocke, N. (2015). Algorithm 954: An accurate and efficient cubic and quartic equation solver for physical applications. ACM Transactions on Mathematical Software (TOMS), 41(4), 1-24. https://doi.org/10.1145/2699468

For quartics, an even newer solver in C is available:

Orellana, A. G., & Michele, C. D. (2020). Algorithm 1010: Boosting Efficiency in Solving Quartic Equations with No Compromise in Accuracy. ACM Transactions on Mathematical Software (TOMS), 46(2), 1-28. https://doi.org/10.1145/3386241

The Zip files don't contain license files, so the ACM Software License Agreement applies.