I've written an ebuild for xppaut, a tool to solve differential equations difference equations, delay equations, functional equations, boundary value problems, and stochastic equations. I think this ebuild needs some rewriting, especially in how CFLAGS are modified, but it actually works.
Created attachment 93123 [details] xppaut ebuild
Please, continue in the pending bug. *** This bug has been marked as a duplicate of 50209 ***