CompositeAlgorithm and switching compatibility about delaydiffeq.jl

[ChrisRackauckas]

I merged master into your branch and fixed the current in the cache and now it's interpolating properly.

[ChrisRackauckas]

@YingboMa letting you know this is working

[devmotion]

I updated the type of the returned solution and added some tests in https://github.com/JuliaDiffEq/DelayDiffEq.jl/tree/composite. However, something seems to be incorrect/broken as the following example of the first Robertson problem in #67 shows:

sol = solve(prob_dde_rober1, MethodOfSteps(AutoTsit5(Rosenbrock23())); initial_order = 1)

all(sol.alg_choice .== 1)

plot(sol)

[ChrisRackauckas]

If you check the solution, at the end the current algorithm should be 2, but all(sol.alg_choice .== 1) is true, so the interpolant is broken since it's using the wrong interpolation.

[ChrisRackauckas]

integrator_utils.jl on line 88 has:

      if typeof(integrator.alg) <: OrdinaryDiffEqCompositeAlgorithm
        copyat_or_push!(integrator.sol.alg_choice,integrator.saveiter,integrator.cache.current)
      end

I don't think we update cache.current in the other cache.

[ChrisRackauckas]

[ChrisRackauckas]

Is the branch missing anything or is it ready to merge? LGTM?

[devmotion]

No, I guess it's complete and ready to merge. Thanks for the fix!

[ChrisRackauckas]

Thank you too. Good team effort 👍