feat: add symbolic tstops support to ODESystem

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -1051,6 +1051,7 @@ for prop in [:eqs
              :split_idxs
              :parent
              :is_dde
+             :tstops
              :index_cache
              :is_scalar_noise
              :isscheduled]
@@ -1377,6 +1378,14 @@ function namespace_initialization_equations(
     map(eq -> namespace_equation(eq, sys; ivs), eqs)
 end
 
+function namespace_tstops(sys::AbstractSystem)
+    tstops = symbolic_tstops(sys)
+    isempty(tstops) && return tstops
+    map(tstops) do val
+        namespace_expr(val, sys)
+    end
+end
+
 function namespace_equation(eq::Equation,
         sys,
         n = nameof(sys);
@@ -1632,6 +1641,14 @@ function initialization_equations(sys::AbstractSystem)
     end
 end
 
+function symbolic_tstops(sys::AbstractSystem)
+    tstops = get_tstops(sys)
+    systems = get_systems(sys)
+    isempty(systems) && return tstops
+    tstops = [tstops; reduce(vcat, namespace_tstops.(get_systems(sys)); init = [])]
+    return tstops
+end
+
 function preface(sys::AbstractSystem)
     has_preface(sys) || return nothing
     pre = get_preface(sys)

src/systems/diffeqs/abstractodesystem.jl

@@ -758,6 +758,39 @@ function DAEFunctionExpr(sys::AbstractODESystem, args...; kwargs...)
     DAEFunctionExpr{true}(sys, args...; kwargs...)
 end
 
+struct SymbolicTstops{F}
+    fn::F
+end
+
+function (st::SymbolicTstops)(p, tspan)
+    unique!(sort!(reduce(vcat, st.fn(p..., tspan...))))
+end
+
+function SymbolicTstops(
+        sys::AbstractSystem; eval_expression = false, eval_module = @__MODULE__)
+    tstops = symbolic_tstops(sys)
+    isempty(tstops) && return nothing
+    t0 = gensym(:t0)
+    t1 = gensym(:t1)
+    tstops = map(tstops) do val
+        if is_array_of_symbolics(val) || val isa AbstractArray
+            collect(val)
+        else
+            term(:, t0, unwrap(val), t1; type = AbstractArray{Real})
+        end
+    end
+    rps = reorder_parameters(sys, parameters(sys))
+    tstops, _ = build_function(tstops,
+        rps...,
+        t0,
+        t1;
+        expression = Val{true},
+        wrap_code = wrap_array_vars(sys, tstops; dvs = nothing) .∘
+                    wrap_parameter_dependencies(sys, false))
+    tstops = eval_or_rgf(tstops; eval_expression, eval_module)
+    return SymbolicTstops(tstops)
+end
+
 """
 ```julia
 DiffEqBase.ODEProblem{iip}(sys::AbstractODESystem, u0map, tspan,
@@ -817,6 +850,11 @@ function DiffEqBase.ODEProblem{iip, specialize}(sys::AbstractODESystem, u0map =
         kwargs1 = merge(kwargs1, (callback = cbs,))
     end
 
+    tstops = SymbolicTstops(sys; eval_expression, eval_module)
+    if tstops !== nothing
+        kwargs1 = merge(kwargs1, (; tstops))
+    end
+
     return ODEProblem{iip}(f, u0, tspan, p, pt; kwargs1..., kwargs...)
 end
 get_callback(prob::ODEProblem) = prob.kwargs[:callback]
@@ -843,7 +881,7 @@ end
 function DiffEqBase.DAEProblem{iip}(sys::AbstractODESystem, du0map, u0map, tspan,
         parammap = DiffEqBase.NullParameters();
         warn_initialize_determined = true,
-        check_length = true, kwargs...) where {iip}
+        check_length = true, eval_expression = false, eval_module = @__MODULE__, kwargs...) where {iip}
     if !iscomplete(sys)
         error("A completed system is required. Call `complete` or `structural_simplify` on the system before creating a `DAEProblem`")
     end
@@ -856,8 +894,15 @@ function DiffEqBase.DAEProblem{iip}(sys::AbstractODESystem, du0map, u0map, tspan
     differential_vars = map(Base.Fix2(in, diffvars), sts)
     kwargs = filter_kwargs(kwargs)
 
+    kwargs1 = (;)
+
+    tstops = SymbolicTstops(sys; eval_expression, eval_module)
+    if tstops !== nothing
+        kwargs1 = merge(kwargs1, (; tstops))
+    end
+
     DAEProblem{iip}(f, du0, u0, tspan, p; differential_vars = differential_vars,
-        kwargs...)
+        kwargs..., kwargs1...)
 end
 
 function generate_history(sys::AbstractODESystem, u0; expression = Val{false}, kwargs...)

src/systems/diffeqs/odesystem.jl

@@ -149,6 +149,11 @@ struct ODESystem <: AbstractODESystem
     """
     is_dde::Bool
     """
+    A list of points to provide to the solver as tstops. Uses the same syntax as discrete
+    events.
+    """
+    tstops::Vector{Any}
+    """
     Cache for intermediate tearing state.
     """
     tearing_state::Any
@@ -187,7 +192,7 @@ struct ODESystem <: AbstractODESystem
             connector_type, preface, cevents,
             devents, parameter_dependencies,
             metadata = nothing, gui_metadata = nothing, is_dde = false,
-            tearing_state = nothing,
+            tstops = [], tearing_state = nothing,
             substitutions = nothing, complete = false, index_cache = nothing,
             discrete_subsystems = nothing, solved_unknowns = nothing,
             split_idxs = nothing, parent = nothing; checks::Union{Bool, Int} = true)
@@ -206,7 +211,7 @@ struct ODESystem <: AbstractODESystem
             ctrl_jac, Wfact, Wfact_t, name, description, systems, defaults, guesses, torn_matching,
             initializesystem, initialization_eqs, schedule, connector_type, preface,
             cevents, devents, parameter_dependencies, metadata,
-            gui_metadata, is_dde, tearing_state, substitutions, complete, index_cache,
+            gui_metadata, is_dde, tstops, tearing_state, substitutions, complete, index_cache,
             discrete_subsystems, solved_unknowns, split_idxs, parent)
     end
 end
@@ -233,7 +238,8 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
         checks = true,
         metadata = nothing,
         gui_metadata = nothing,
-        is_dde = nothing)
+        is_dde = nothing,
+        tstops = [])
     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."
@@ -299,7 +305,7 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
         defaults, guesses, nothing, initializesystem,
         initialization_eqs, schedule, connector_type, preface, cont_callbacks,
         disc_callbacks, parameter_dependencies,
-        metadata, gui_metadata, is_dde, checks = checks)
+        metadata, gui_metadata, is_dde, tstops, checks = checks)
 end
 
 function ODESystem(eqs, iv; kwargs...)
@@ -402,6 +408,7 @@ function flatten(sys::ODESystem, noeqs = false)
             description = description(sys),
             initialization_eqs = initialization_equations(sys),
             is_dde = is_dde(sys),
+            tstops = symbolic_tstops(sys),
             checks = false)
     end
 end

test/odesystem.jl

@@ -1524,3 +1524,31 @@ end
     sol = solve(prob, DFBDF(), abstol=1e-8, reltol=1e-8)
     @test sol[x]≈sol[y^2 - sum(p)] atol=1e-5
 end
+
+@testset "Symbolic tstops" begin
+    @variables x(t) = 1.0
+    @parameters p=0.15 q=0.25 r[1:2]=[0.35, 0.45]
+    @mtkbuild sys = ODESystem(
+        [D(x) ~ p * x + q * t + sum(r)], t; tstops = [0.5p, [0.1, 0.2], [p + 2q], r])
+    prob = ODEProblem(sys, [], (0.0, 5.0))
+    sol = solve(prob)
+    expected_tstops = unique!(sort!(vcat(0.0:0.075:5.0, 0.1, 0.2, 0.65, 0.35, 0.45)))
+    @test all(x -> any(isapprox(x, atol = 1e-6), sol.t), expected_tstops)
+    prob2 = remake(prob; tspan = (0.0, 10.0))
+    sol2 = solve(prob2)
+    expected_tstops = unique!(sort!(vcat(0.0:0.075:10.0, 0.1, 0.2, 0.65, 0.35, 0.45)))
+    @test all(x -> any(isapprox(x, atol = 1e-6), sol2.t), expected_tstops)
+
+    @variables y(t) [guess = 1.0]
+    @mtkbuild sys = ODESystem([D(x) ~ p * x + q * t + sum(r), y^3 ~ 2x + 1],
+        t; tstops = [0.5p, [0.1, 0.2], [p + 2q], r])
+    prob = DAEProblem(
+        sys, [D(y) => 2D(x) / 3y^2, D(x) => p * x + q * t + sum(r)], [], (0.0, 5.0))
+    sol = solve(prob, DImplicitEuler())
+    expected_tstops = unique!(sort!(vcat(0.0:0.075:5.0, 0.1, 0.2, 0.65, 0.35, 0.45)))
+    @test all(x -> any(isapprox(x, atol = 1e-6), sol.t), expected_tstops)
+    prob2 = remake(prob; tspan = (0.0, 10.0))
+    sol2 = solve(prob2, DImplicitEuler())
+    expected_tstops = unique!(sort!(vcat(0.0:0.075:10.0, 0.1, 0.2, 0.65, 0.35, 0.45)))
+    @test all(x -> any(isapprox(x, atol = 1e-6), sol2.t), expected_tstops)
+end