Optim, NLsolve and LsqFit are three packages in the JuliaNLSolvers organization. They have all been around from the early Julia days, and serve some basic scientific computing needs such as minimizing a function, fitting a curve and solving a system of equations. Their age means that they are widely used and well-known. However, their age also show in much of the design and abstractions that predates many of the unique and powerful features and packages in Julia.

Based on my own experience as a maintainer of these packages, and learning from the discussions on mailing lists, forums, and github, I will talk about the failures of the three packages, and how a complete rewrite of the packages is the best way forward. Hopefully, my reflections and experiences can help future package writers avoid making the same mistakes over and over again.

The talk won't be heavy on the mathematical details, but will explore important things to design for from the start. Users will eventually request many of the features, but they might be difficult to retrofit, so come join the quest to find the best ways of satisfying the greedy Julia users and abusers out there!