feat: add is_dde flag for ODESystem and SDESystem

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -971,6 +971,7 @@ for prop in [:eqs
              :solved_unknowns
              :split_idxs
              :parent
+             :is_dde
              :index_cache
              :is_scalar_noise
              :isscheduled]

src/systems/diffeqs/abstractodesystem.jl

@@ -3,6 +3,29 @@ struct Schedule
     dummy_sub::Any
 end
 
+"""
+    is_dde(sys::AbstractSystem)
+
+Return a boolean indicating whether a system represents a set of delay
+differential equations.
+"""
+is_dde(sys::AbstractSystem) = has_is_dde(sys) && get_is_dde(sys)
+
+function _check_if_dde(eqs, iv, subsystems)
+    is_dde = any(ModelingToolkit.is_dde, subsystems)
+    if !is_dde
+        vs = Set()
+        for eq in eqs
+            vars!(vs, eq)
+            is_dde = any(vs) do sym
+                isdelay(unwrap(sym), iv)
+            end
+            is_dde && break
+        end
+    end
+    return is_dde
+end
+
 function filter_kwargs(kwargs)
     kwargs = Dict(kwargs)
     for key in keys(kwargs)

src/systems/diffeqs/odesystem.jl

@@ -141,6 +141,10 @@ struct ODESystem <: AbstractODESystem
     """
     gui_metadata::Union{Nothing, GUIMetadata}
     """
+    A boolean indicating if the given `ODESystem` represents a system of DDEs.
+    """
+    is_dde::Bool
+    """
     Cache for intermediate tearing state.
     """
     tearing_state::Any
@@ -178,7 +182,7 @@ struct ODESystem <: AbstractODESystem
             torn_matching, initializesystem, initialization_eqs, schedule,
             connector_type, preface, cevents,
             devents, parameter_dependencies,
-            metadata = nothing, gui_metadata = nothing,
+            metadata = nothing, gui_metadata = nothing, is_dde = false,
             tearing_state = nothing,
             substitutions = nothing, complete = false, index_cache = nothing,
             discrete_subsystems = nothing, solved_unknowns = nothing,
@@ -198,7 +202,7 @@ struct ODESystem <: AbstractODESystem
             ctrl_jac, Wfact, Wfact_t, name, systems, defaults, guesses, torn_matching,
             initializesystem, initialization_eqs, schedule, connector_type, preface,
             cevents, devents, parameter_dependencies, metadata,
-            gui_metadata, tearing_state, substitutions, complete, index_cache,
+            gui_metadata, is_dde, tearing_state, substitutions, complete, index_cache,
             discrete_subsystems, solved_unknowns, split_idxs, parent)
     end
 end
@@ -223,7 +227,8 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
         parameter_dependencies = Equation[],
         checks = true,
         metadata = nothing,
-        gui_metadata = nothing)
+        gui_metadata = nothing,
+        is_dde = nothing)
     name === nothing &&
         throw(ArgumentError("The `name` keyword must be provided. Please consider using the `@named` macro"))
     @assert all(control -> any(isequal.(control, ps)), controls) "All controls must also be parameters."
@@ -266,12 +271,15 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
     disc_callbacks = SymbolicDiscreteCallbacks(discrete_events)
     parameter_dependencies, ps′ = process_parameter_dependencies(
         parameter_dependencies, ps′)
+    if is_dde === nothing
+        is_dde = _check_if_dde(deqs, iv′, systems)
+    end
     ODESystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
         deqs, iv′, dvs′, ps′, tspan, var_to_name, ctrl′, observed, tgrad, jac,
         ctrl_jac, Wfact, Wfact_t, name, systems, defaults, guesses, nothing, initializesystem,
         initialization_eqs, schedule, connector_type, preface, cont_callbacks,
         disc_callbacks, parameter_dependencies,
-        metadata, gui_metadata, checks = checks)
+        metadata, gui_metadata, is_dde, checks = checks)
 end
 
 function ODESystem(eqs, iv; kwargs...)

src/systems/diffeqs/sdesystem.jl

@@ -133,6 +133,10 @@ struct SDESystem <: AbstractODESystem
     be `true` when `noiseeqs isa Vector`. 
     """
     is_scalar_noise::Bool
+    """
+    A boolean indicating if the given `ODESystem` represents a system of DDEs.
+    """
+    is_dde::Bool
     isscheduled::Bool
 
     function SDESystem(tag, deqs, neqs, iv, dvs, ps, tspan, var_to_name, ctrls, observed,
@@ -141,6 +145,7 @@ struct SDESystem <: AbstractODESystem
             ctrl_jac, Wfact, Wfact_t, name, systems, defaults, connector_type,
             cevents, devents, parameter_dependencies, metadata = nothing, gui_metadata = nothing,
             complete = false, index_cache = nothing, parent = nothing, is_scalar_noise = false,
+            is_dde = false,
             isscheduled = false;
             checks::Union{Bool, Int} = true)
         if checks == true || (checks & CheckComponents) > 0
@@ -165,7 +170,7 @@ struct SDESystem <: AbstractODESystem
             ctrl_jac,
             Wfact, Wfact_t, name, systems, defaults, connector_type, cevents, devents,
             parameter_dependencies, metadata, gui_metadata, complete, index_cache, parent, is_scalar_noise,
-            isscheduled)
+            is_dde, isscheduled)
     end
 end
 
@@ -188,7 +193,8 @@ function SDESystem(deqs::AbstractVector{<:Equation}, neqs::AbstractArray, iv, dv
         complete = false,
         index_cache = nothing,
         parent = nothing,
-        is_scalar_noise = false)
+        is_scalar_noise = false,
+        is_dde = nothing)
     name === nothing &&
         throw(ArgumentError("The `name` keyword must be provided. Please consider using the `@named` macro"))
     iv′ = value(iv)
@@ -223,11 +229,14 @@ function SDESystem(deqs::AbstractVector{<:Equation}, neqs::AbstractArray, iv, dv
     disc_callbacks = SymbolicDiscreteCallbacks(discrete_events)
     parameter_dependencies, ps′ = process_parameter_dependencies(
         parameter_dependencies, ps′)
+    if is_dde === nothing
+        is_dde = _check_if_dde(deqs, iv′, systems)
+    end
     SDESystem(Threads.atomic_add!(SYSTEM_COUNT, UInt(1)),
         deqs, neqs, iv′, dvs′, ps′, tspan, var_to_name, ctrl′, observed, tgrad, jac,
         ctrl_jac, Wfact, Wfact_t, name, systems, defaults, connector_type,
         cont_callbacks, disc_callbacks, parameter_dependencies, metadata, gui_metadata,
-        complete, index_cache, parent, is_scalar_noise; checks = checks)
+        complete, index_cache, parent, is_scalar_noise, is_dde; checks = checks)
 end
 
 function SDESystem(sys::ODESystem, neqs; kwargs...)

test/dde.jl

@@ -38,6 +38,7 @@ eqs = [D(x₀) ~ (v0 / (1 + beta0 * (x₂(t - tau)^2))) * (p0 - q0) * x₀ - d0
                (v1 / (1 + beta1 * (x₂(t - tau)^2))) * (p1 - q1) * x₁ - d1 * x₁
        D(x₂(t)) ~ (v1 / (1 + beta1 * (x₂(t - tau)^2))) * (1 - p1 + q1) * x₁ - d2 * x₂(t)]
 @mtkbuild sys = System(eqs, t)
+@test ModelingToolkit.is_dde(sys)
 prob = DDEProblem(sys,
     [x₀ => 1.0, x₁ => 1.0, x₂(t) => 1.0],
     tspan,
@@ -77,6 +78,7 @@ sol = solve(prob, RKMil())
 τ = 1.0
 eqs = [D(x(t)) ~ a * x(t) + b * x(t - τ) + c + (α * x(t) + γ) * η]
 @mtkbuild sys = System(eqs, t)
+@test ModelingToolkit.is_dde(sys)
 @test equations(sys) == [D(x(t)) ~ a * x(t) + b * x(t - τ) + c]
 @test isequal(ModelingToolkit.get_noiseeqs(sys), [α * x(t) + γ])
 prob_mtk = SDDEProblem(sys, [x(t) => 1.0 + t], tspan; constant_lags = (τ,));
@@ -100,8 +102,11 @@ end
 eqs = [osc1.jcn ~ osc2.delx,
     osc2.jcn ~ osc1.delx]
 @named coupledOsc = System(eqs, t)
+@test ModelingToolkit.is_dde(coupledOsc)
 @named coupledOsc = compose(coupledOsc, systems)
+@test ModelingToolkit.is_dde(coupledOsc)
 @named coupledOsc2 = System(eqs, t; systems)
+@test ModelingToolkit.is_dde(coupledOsc2)
 for coupledOsc in [coupledOsc, coupledOsc2]
     local sys = structural_simplify(coupledOsc)
     @test length(equations(sys)) == 4

test/odesystem.jl

@@ -1394,3 +1394,11 @@ end
     prob = @test_nowarn ODEProblem(sys, nothing, (0.0, 1.0))
     @test_nowarn solve(prob)
 end
+
+@testset "ODEs are not DDEs" begin
+    @variables x(t)
+    @named sys = ODESystem(D(x) ~ x, t)
+    @test !ModelingToolkit.is_dde(sys)
+    @named sys2 = ODESystem(Equation[], t; systems = [sys])
+    @test !ModelingToolkit.is_dde(sys)
+end