Apply changes to ExponentialUtilities.jl to the ExpRK integrators

[MSeeker1340]

SciML/ExponentialUtilities.jl#1

Currently the only breaking change is the dropping of cache in expv(!) and phiv(!).

[ChrisRackauckas]

How do you plan to do the breaking change?

[MSeeker1340]

For now fc257d5 will do. Since @jagot is still actively developing on his part I would expect more breaking changes in the future, at which point I'll implement those in OrdinaryDiffEq along the way. And after that we can merge the branch and push a release for both ExponentialUtilities and OrdinaryDiffEq.

[ChrisRackauckas]

That's fine if ExponentialUtilities.jl gets a major version bump and if we bump the minimum required version here to that major version. For compatibility, it should pass through a no-op that drops the cache argument, but it's fine. If the cache argument isn't passed anymore, where does the cache array come from? I assume it's just allocated now?

[MSeeker1340]

It now uses the next column of the V matrix as the cache and thus eliminates the need for external caches.

For compatibility, it should pass through a no-op that drops the cache argument, but it's fine.

@jagot can you do this alongside whatever's next in your plate? Just add back the cache argument and document somewhere about future deprecation?

[MSeeker1340]

Resolved as of https://github.com/JuliaDiffEq/OrdinaryDiffEq.jl/tree/v4.15.1.