Fix #911

Author: YingboMa

Project.toml

@@ -1,7 +1,7 @@
 name = "ModelingToolkit"
 uuid = "961ee093-0014-501f-94e3-6117800e7a78"
 authors = ["Chris Rackauckas <[email protected]>"]
-version = "5.13.5"
+version = "5.13.6"
 
 [deps]
 ArrayInterface = "4fba245c-0d91-5ea0-9b3e-6abc04ee57a9"

src/systems/diffeqs/modelingtoolkitize.jl

@@ -14,10 +14,11 @@ function modelingtoolkitize(prob::DiffEqBase.ODEProblem)
         p = prob.p
     end
 
+    has_p = !(p isa Union{DiffEqBase.NullParameters,Nothing})
+
     var(x, i) = Num(Sym{FnType{Tuple{symtype(t)}, Real}}(nameof(Variable(x, i))))
     vars = ArrayInterface.restructure(prob.u0,[var(:x, i)(ModelingToolkit.value(t)) for i in eachindex(prob.u0)])
-    params = p isa DiffEqBase.NullParameters ? [] :
-             reshape([Num(Sym{Real}(nameof(Variable(:α, i)))) for i in eachindex(p)],size(p))
+    params = has_p ? reshape([Num(Sym{Real}(nameof(Variable(:α, i)))) for i in eachindex(p)],size(p)) : []
     var_set = Set(vars)
 
     D = Differential(t)
@@ -52,10 +53,12 @@ function modelingtoolkitize(prob::DiffEqBase.ODEProblem)
     else
         vec(collect(params))
     end
+    default_u0 = Dict(sts .=> vec(collect(prob.u0)))
+    default_p = has_p ? Dict(params .=> vec(collect(prob.p))) : Dict()
 
     de = ODESystem(
         eqs, t, sts, params,
-        defaults=merge(Dict(sts .=> vec(collect(prob.u0))), Dict(params .=> vec(collect(prob.p)))),
+        defaults=merge(default_u0, default_p),
     )
 
     de

test/modelingtoolkitize.jl

@@ -185,3 +185,10 @@ prob = ODEProblem(pendulum_sys, Pair[], tspan)
 sol = solve(prob, Rodas4())
 l2 = sol[sts[1]].^2 + sol[sts[3]].^2
 @test all(l->abs(sqrt(l) - 1) < 0.05, l2)
+
+ff911 = (du,u,p,t) -> begin
+    du[1] = u[2] + 1.0
+    du[2] = u[1] - 1.0
+end
+prob = ODEProblem(ff911, zeros(2), (0, 1.0))
+@test_nowarn modelingtoolkitize(prob)