preserve sys in ODEFunction from ODAEProblem (#1883)

Author: anandijain

src/structural_transformation/codegen.jl

@@ -342,7 +342,8 @@ function build_torn_function(sys;
                                                     paramsyms = Symbol.(parameters(sys)),
                                                     indepsym = Symbol(get_iv(sys)),
                                                     observed = observedfun,
-                                                    mass_matrix = mass_matrix), states
+                                                    mass_matrix = mass_matrix,
+                                                    sys = sys), states
     end
 end
 

test/odesystem.jl

@@ -910,3 +910,16 @@ else
     @test_throws "-cos(Q(t))" prob.f(du, [1, 0], prob.p, 0.0)
     @test_throws "sin(P(t))" prob.f(du, [0, 2], prob.p, 0.0)
 end
+
+let
+    @variables t
+    D = Differential(t)
+    @variables x(t) = 1
+    @variables y(t) = 1
+    @parameters pp = -1
+    der = Differential(t)
+    @named sys4 = ODESystem([der(x) ~ -y; der(y) ~ 1 + pp * y + x], t)
+    sys4s = structural_simplify(sys4)
+    prob = ODAEProblem(sys4s, [x => 1.0, D(x) => 1.0], (0, 1.0))
+    @test !isnothing(prob.f.sys)
+end