Add support for an external synchronous compiler to discrete and hybrid systems

src/clock.jl

@@ -1,11 +1,15 @@
 @data InferredClock begin
     Inferred
-    InferredDiscrete
+    InferredDiscrete(Int)
 end
 
 const InferredTimeDomain = InferredClock.Type
 using .InferredClock: Inferred, InferredDiscrete
 
+function InferredClock.InferredDiscrete()
+    return InferredDiscrete(0)
+end
+
 Base.Broadcast.broadcastable(x::InferredTimeDomain) = Ref(x)
 
 struct VariableTimeDomain end
@@ -50,7 +54,7 @@ has_time_domain(x::Num) = has_time_domain(value(x))
 has_time_domain(x) = false
 
 for op in [Differential]
-    @eval input_timedomain(::$op, arg = nothing) = ContinuousClock()
+    @eval input_timedomain(::$op, arg = nothing) = (ContinuousClock(),)
     @eval output_timedomain(::$op, arg = nothing) = ContinuousClock()
 end
 
@@ -97,6 +101,7 @@ function is_discrete_domain(x)
 end
 
 sampletime(c) = Moshi.Match.@match c begin
+    x::SciMLBase.AbstractClock => nothing
     PeriodicClock(dt) => dt
     _ => nothing
 end

src/discretedomain.jl

@@ -10,6 +10,20 @@ are not transparent but `Sample` and `Hold` are. Defaults to `false` if not impl
 is_transparent_operator(x) = is_transparent_operator(typeof(x))
 is_transparent_operator(::Type) = false
 
+"""
+    $(TYPEDSIGNATURES)
+
+Trait to be implemented for operators which determines whether the operator is applied to
+a time-varying quantity and results in a time-varying quantity. For example, `Initial` and
+`Pre` are not time-varying since while they are applied to variables, the application
+results in a non-discrete-time parameter. `Differential`, `Shift`, `Sample` and `Hold` are
+all time-varying operators. All time-varying operators must implement `input_timedomain` and
+`output_timedomain`.
+"""
+is_timevarying_operator(x) = is_timevarying_operator(typeof(x))
+is_timevarying_operator(::Type{<:Symbolics.Operator}) = true
+is_timevarying_operator(::Type) = false
+
 """
     function SampleTime()
 
@@ -314,12 +328,13 @@ Base.:-(k::ShiftIndex, i::Int) = k + (-i)
     input_timedomain(op::Operator)
 
 Return the time-domain type (`ContinuousClock()` or `InferredDiscrete()`) that `op` operates on.
+Should return a tuple containing the time domain type for each argument to the operator.
 """
 function input_timedomain(s::Shift, arg = nothing)
     if has_time_domain(arg)
         return get_time_domain(arg)
     end
-    InferredDiscrete()
+    (InferredDiscrete(),)
 end
 
 """
@@ -334,34 +349,45 @@ function output_timedomain(s::Shift, arg = nothing)
     InferredDiscrete()
 end
 
-input_timedomain(::Sample, _ = nothing) = ContinuousClock()
+input_timedomain(::Sample, _ = nothing) = (ContinuousClock(),)
 output_timedomain(s::Sample, _ = nothing) = s.clock
 
 function input_timedomain(h::Hold, arg = nothing)
     if has_time_domain(arg)
         return get_time_domain(arg)
     end
-    InferredDiscrete() # the Hold accepts any discrete
+    (InferredDiscrete(),) # the Hold accepts any discrete
 end
 output_timedomain(::Hold, _ = nothing) = ContinuousClock()
 
 sampletime(op::Sample, _ = nothing) = sampletime(op.clock)
 sampletime(op::ShiftIndex, _ = nothing) = sampletime(op.clock)
 
-changes_domain(op) = isoperator(op, Union{Sample, Hold})
-
 function output_timedomain(x)
     if isoperator(x, Operator)
-        return output_timedomain(operation(x), arguments(x)[])
+        args = arguments(x)
+        return output_timedomain(operation(x), if length(args) == 1 args[] else args end)
     else
         throw(ArgumentError("$x of type $(typeof(x)) is not an operator expression"))
     end
 end
 
 function input_timedomain(x)
     if isoperator(x, Operator)
-        return input_timedomain(operation(x), arguments(x)[])
+        args = arguments(x)
+        return input_timedomain(operation(x), if length(args) == 1 args[] else args end)
     else
         throw(ArgumentError("$x of type $(typeof(x)) is not an operator expression"))
     end
 end
+
+function ZeroCrossing(expr; name = gensym(), up = true, down = true, kwargs...)
+    return SymbolicContinuousCallback(
+        [expr ~ 0], up ? ImperativeAffect(Returns(nothing)) : nothing;
+        affect_neg = down ? ImperativeAffect(Returns(nothing)) : nothing,
+        kwargs..., zero_crossing_id = name)
+end
+
+function SciMLBase.Clocks.EventClock(cb::SymbolicContinuousCallback)
+    return SciMLBase.Clocks.EventClock(cb.zero_crossing_id)
+end

src/systems/abstractsystem.jl

@@ -486,13 +486,12 @@ The `Initial` operator. Used by initialization to store constant constraints on
 of a system. See the documentation section on initialization for more information.
 """
 struct Initial <: Symbolics.Operator end
+is_timevarying_operator(::Type{Initial}) = false
 Initial(x) = Initial()(x)
 SymbolicUtils.promote_symtype(::Type{Initial}, T) = T
 SymbolicUtils.isbinop(::Initial) = false
 Base.nameof(::Initial) = :Initial
 Base.show(io::IO, x::Initial) = print(io, "Initial")
-input_timedomain(::Initial, _ = nothing) = ContinuousClock()
-output_timedomain(::Initial, _ = nothing) = ContinuousClock()
 
 function (f::Initial)(x)
     # wrap output if wrapped input
@@ -1228,6 +1227,7 @@ function namespace_expr(
         O
     end
 end
+
 _nonum(@nospecialize x) = x isa Num ? x.val : x
 
 """

src/systems/callbacks.jl

@@ -56,12 +56,11 @@ before the callback is triggered.
 """
 struct Pre <: Symbolics.Operator end
 Pre(x) = Pre()(x)
+is_timevarying_operator(::Type{Pre}) = false
 SymbolicUtils.promote_symtype(::Type{Pre}, T) = T
 SymbolicUtils.isbinop(::Pre) = false
 Base.nameof(::Pre) = :Pre
 Base.show(io::IO, x::Pre) = print(io, "Pre")
-input_timedomain(::Pre, _ = nothing) = ContinuousClock()
-output_timedomain(::Pre, _ = nothing) = ContinuousClock()
 unPre(x::Num) = unPre(unwrap(x))
 unPre(x::Symbolics.Arr) = unPre(unwrap(x))
 unPre(x::Symbolic) = (iscall(x) && operation(x) isa Pre) ? only(arguments(x)) : x
@@ -165,6 +164,7 @@ struct SymbolicContinuousCallback <: AbstractCallback
     finalize::Union{Affect, Nothing}
     rootfind::Union{Nothing, SciMLBase.RootfindOpt}
     reinitializealg::SciMLBase.DAEInitializationAlgorithm
+    zero_crossing_id::Symbol
 
     function SymbolicContinuousCallback(
             conditions::Union{Equation, Vector{Equation}},
@@ -174,6 +174,7 @@ struct SymbolicContinuousCallback <: AbstractCallback
             finalize = nothing,
             rootfind = SciMLBase.LeftRootFind,
             reinitializealg = nothing,
+            zero_crossing_id = gensym(),
             kwargs...)
         conditions = (conditions isa AbstractVector) ? conditions : [conditions]
 
@@ -190,7 +191,7 @@ struct SymbolicContinuousCallback <: AbstractCallback
             make_affect(affect_neg; kwargs...),
             make_affect(initialize; kwargs...), make_affect(
                 finalize; kwargs...),
-            rootfind, reinitializealg)
+            rootfind, reinitializealg, zero_crossing_id)
     end # Default affect to nothing
 end
 
@@ -466,7 +467,8 @@ function namespace_callback(cb::SymbolicContinuousCallback, s)::SymbolicContinuo
         affect_neg = namespace_affects(affect_negs(cb), s),
         initialize = namespace_affects(initialize_affects(cb), s),
         finalize = namespace_affects(finalize_affects(cb), s),
-        rootfind = cb.rootfind, reinitializealg = cb.reinitializealg)
+        rootfind = cb.rootfind, reinitializealg = cb.reinitializealg,
+        zero_crossing_id = cb.zero_crossing_id)
 end
 
 function namespace_conditions(condition, s)
@@ -490,6 +492,8 @@ function Base.hash(cb::AbstractCallback, s::UInt)
     s = hash(finalize_affects(cb), s)
     !is_discrete(cb) && (s = hash(cb.rootfind, s))
     hash(cb.reinitializealg, s)
+    !is_discrete(cb) && (s = hash(cb.zero_crossing_id, s))
+    return s
 end
 
 ###########################
@@ -524,13 +528,16 @@ function finalize_affects(cbs::Vector{<:AbstractCallback})
 end
 
 function Base.:(==)(e1::AbstractCallback, e2::AbstractCallback)
-    (is_discrete(e1) === is_discrete(e2)) || return false
-    (isequal(e1.conditions, e2.conditions) && isequal(e1.affect, e2.affect) &&
-     isequal(e1.initialize, e2.initialize) && isequal(e1.finalize, e2.finalize)) &&
-        isequal(e1.reinitializealg, e2.reinitializealg) ||
-        return false
-    is_discrete(e1) ||
-        (isequal(e1.affect_neg, e2.affect_neg) && isequal(e1.rootfind, e2.rootfind))
+    is_discrete(e1) === is_discrete(e2) || return false
+    isequal(e1.conditions, e2.conditions) && isequal(e1.affect, e2.affect) || return false
+    isequal(e1.initialize, e2.initialize) || return false
+    isequal(e1.finalize, e2.finalize) || return false
+    isequal(e1.reinitializealg, e2.reinitializealg) || return false
+    if !is_discrete(e1)
+        isequal(e1.affect_neg, e2.affect_neg) || return false
+        isequal(e1.rootfind, e2.rootfind) || return false
+        isequal(e1.zero_crossing_id, e2.zero_crossing_id) || return false
+    end
 end
 
 Base.isempty(cb::AbstractCallback) = isempty(cb.conditions)