Sondar74

Results 3 issues of Sondar74

I have cleaned the previous PR and just kept the `nonlinear_constraints` file.

New PR with tolerances. Added absolute tolerance for `isapprox()` and exact comparison for `Rational` inputs. New PR with one test for a RK method with Floating Inputs obtained from MatLab....

This code is based on the paper "A characterization of energy-preserving methods and the construction of parallel integrators for Hamiltonian systems" (https://doi.org/10.48550/arXiv.1505.02537). Added a struct in BSeries.jl called ContinuousStageRungeKutta and...