fix: support non-tunable parameters with DDEs

Author: AayushSabharwal

src/systems/diffeqs/abstractodesystem.jl

@@ -189,7 +189,9 @@ function generate_function(sys::AbstractODESystem, dvs = unknowns(sys),
         wrap_code = identity,
         kwargs...)
     if isdde
-        eqs = delay_to_function(sys)
+        issplit = has_index_cache(sys) && get_index_cache(sys) !== nothing
+        eqs = delay_to_function(
+            sys; history_arg = issplit ? MTKPARAMETERS_ARG : DEFAULT_PARAMS_ARG)
     else
         eqs = [eq for eq in equations(sys)]
     end
@@ -211,7 +213,10 @@ function generate_function(sys::AbstractODESystem, dvs = unknowns(sys),
     t = get_iv(sys)
 
     if isdde
-        build_function(rhss, u, DDE_HISTORY_FUN, p..., t; kwargs...)
+        build_function(rhss, u, DDE_HISTORY_FUN, p..., t; kwargs...,
+            wrap_code = wrap_code .∘ wrap_mtkparameters(sys, false, 3) .∘
+                        wrap_array_vars(sys, rhss; dvs, ps) .∘
+                        wrap_parameter_dependencies(sys, false))
     else
         pre, sol_states = get_substitutions_and_solved_unknowns(sys)
 
@@ -570,9 +575,7 @@ function DiffEqBase.DDEFunction{iip}(sys::AbstractODESystem, dvs = unknowns(sys)
         kwargs...)
     f_oop, f_iip = eval_or_rgf.(f_gen; eval_expression, eval_module)
     f(u, h, p, t) = f_oop(u, h, p, t)
-    f(u, h, p::MTKParameters, t) = f_oop(u, h, p..., t)
     f(du, u, h, p, t) = f_iip(du, u, h, p, t)
-    f(du, u, h, p::MTKParameters, t) = f_iip(du, u, h, p..., t)
 
     DDEFunction{iip}(f, sys = sys)
 end

test/dde.jl

@@ -170,3 +170,20 @@ prob_sa = DDEProblem(sys, [], (0.0, 10.0); constant_lags = [sys.osc1.τ, sys.osc
           sol(sol.t .- prob.ps[ssys.valve.τ]; idxs = ssys.valve.opening).u .+
           sum.(sol[ssys.vvecs.x])
 end
+
+@testset "Issue#3165 DDEs with non-tunables" begin
+    @variables x(..) = 1.0
+    @parameters w=1.0 [tunable = false] τ=0.5
+    eqs = [D(x(t)) ~ -w * x(t - τ)]
+
+    @named sys = System(eqs, t)
+    sys = structural_simplify(sys)
+
+    prob = DDEProblem(sys,
+        [],
+        (0.0, 10.0),
+        constant_lags = [τ])
+
+    alg = MethodOfSteps(Vern7())
+    @test_nowarn solve(prob, alg)
+end