Hello,

I am looking for a constructor for `SplitFunction`

for `SplitODEProblem`

in DifferentialEquations.jl https://docs.sciml.ai/latest/types/split_ode_types/

Given `f1`

and `f2`

, how do you define the corresponding `SplitFunction`

. Here is an example of what I would like to do:

```
using ApproxFun
using DifferentialEquations
S = Fourier(0..16*π)
n = 128
x = points(S, n)
D2 = Derivative(S,2)[1:n,1:n]
D = (Derivative(S) → S)[1:n,1:n]
T = ApproxFun.plan_transform(S, n)
Ti = ApproxFun.plan_itransform(S, n)
D4 = Derivative(S,4)[1:n,1:n]
û₀ = T*(cos.(x/16).*(1 .+ sin.(x/16)))
tmp=similar(û₀)
q = (D,T,Ti,tmp,similar(tmp),similar(tmp))
function kuramoto_sivashinsky(dû,û,q,t)
D,T,Ti,tmp,u,uc = q
mul!(u, D, û)
mul!(tmp, Ti, u)
mul!(u, Ti, û)
@. tmp=tmp*u
mul!(u,T, tmp)
#mul!(uc, D2, û)
@. dû = - u
end
prob = SplitODEProblem(DiffEqArrayOperator(-Diagonal(D4+D2)), kuramoto_sivashinsky, û₀, (0.0,300.0), q)
# What I would like to do
f = SplitFunction(DiffEqArrayOperator(-Diagonal(D4+D2)), kuramoto_sivashinsky)
prob = SplitODEProblem(f, û₀, (0.0,300.0), q)
sol = solve(prob,ETDRK4(), dt = 0.01)
```