I’m working through the first example in the Ordinary Differential Equations section of DifferentialEquations.jl documentation, and when I call solve(prob,Tsit5(),reltol=1e-8,abstol=1e-8), I get

MethodError: no method matching f(::Float64, ::DiffEqBase.NullParameters, ::Float64)

I think at one point, the function signature looked like f(t,u), similar to the MATLAB convention, but it has since changed to f(u,p,t) (or f(du,u,p,t) for the in-place version). If you’re looking at documentation that still has f(t,u), it’s out of date.