Merge pull request #2630 from vyudu/handle_u0_nothing

ImplicitDiscreteSolve: handle case where u is nothing

Author: ChrisRackauckas

lib/ImplicitDiscreteSolve/src/cache.jl

@@ -1,5 +1,5 @@
 mutable struct ImplicitDiscreteState{uType, pType, tType}
-    u::Vector{uType}
+    u::uType
     p::pType
     t_next::tType
 end
@@ -16,7 +16,7 @@ function alg_cache(alg::SimpleIDSolve, u, rate_prototype, ::Type{uEltypeNoUnits}
         dt, reltol, p, calck,
         ::Val{true}) where {uEltypeNoUnits, uBottomEltypeNoUnits, tTypeNoUnits}
 
-    state = ImplicitDiscreteState(similar(u), p, t)
+    state = ImplicitDiscreteState(isnothing(u) ? nothing : zero(u), p, t)
     SimpleIDSolveCache(u, uprev, state, nothing)
 end
 
@@ -31,7 +31,7 @@ function alg_cache(alg::SimpleIDSolve, u, rate_prototype, ::Type{uEltypeNoUnits}
         dt, reltol, p, calck,
         ::Val{false}) where {uEltypeNoUnits, uBottomEltypeNoUnits, tTypeNoUnits}
 
-    state = ImplicitDiscreteState(similar(u), p, t)
+    state = ImplicitDiscreteState(isnothing(u) ? nothing : zero(u), p, t)
     SimpleIDSolveCache(u, uprev, state, nothing)
 end
 

lib/ImplicitDiscreteSolve/src/solve.jl

@@ -12,7 +12,7 @@ function perform_step!(integrator, cache::SimpleIDSolveCache, repeat_step = fals
 end
 
 function initialize!(integrator, cache::SimpleIDSolveCache)
-    cache.state.u .= integrator.u
+    integrator.u isa AbstractVector && (cache.state.u .= integrator.u)
     cache.state.p = integrator.p
     cache.state.t_next = integrator.t
     f = integrator.f
@@ -33,6 +33,7 @@ end
 
 function _initialize_dae!(integrator, prob::ImplicitDiscreteProblem,
         alg::DefaultInit, x::Union{Val{true}, Val{false}})
+    isnothing(prob.u0) && return
     atol = one(eltype(prob.u0)) * 1e-12
     if SciMLBase.has_initializeprob(prob.f)
         _initialize_dae!(integrator, prob,

lib/ImplicitDiscreteSolve/test/runtests.jl

@@ -65,7 +65,17 @@ end
 
     for ts in 1:tsteps
         step!(integ)
-        @show integ.u
         @test integ.u[1]^2 + integ.u[2]^2 ≈ 16
     end
 end
+
+@testset "Handle nothing in u0" begin
+    function empty(u_next, u, p, t) 
+        nothing
+    end
+
+    tsteps = 5
+    u0 = nothing
+    idprob = ImplicitDiscreteProblem(empty, u0, (0, tsteps), [])
+    @test_nowarn integ = init(idprob, SimpleIDSolve())
+end