feat: add substitute_component

Author: AayushSabharwal

src/ModelingToolkit.jl

@@ -291,7 +291,7 @@ export isinput, isoutput, getbounds, hasbounds, getguess, hasguess, isdisturbanc
        hasunit, getunit, hasconnect, getconnect,
        hasmisc, getmisc, state_priority
 export ode_order_lowering, dae_order_lowering, liouville_transform,
-       change_independent_variable
+       change_independent_variable, substitute_component
 export PDESystem
 export Differential, expand_derivatives, @derivatives
 export Equation, ConstrainedEquation

src/systems/abstractsystem.jl

@@ -3181,3 +3181,180 @@ has_diff_eqs(osys21) # returns `false`.
 ```
 """
 has_diff_eqs(sys::AbstractSystem) = any(is_diff_equation, get_eqs(sys))
+
+"""
+    $(TYPEDSIGNATURES)
+
+Validate the rules for replacement of subcomponents as defined in `substitute_component`.
+"""
+function validate_replacement_rule(
+        rule::Pair{T, T}; namespace = []) where {T <: AbstractSystem}
+    lhs, rhs = rule
+
+    iscomplete(lhs) && throw(ArgumentError("LHS of replacement rule cannot be completed."))
+    iscomplete(rhs) && throw(ArgumentError("RHS of replacement rule cannot be completed."))
+
+    rhs_h = namespace_hierarchy(nameof(rhs))
+    if length(rhs_h) != 1
+        throw(ArgumentError("RHS of replacement rule must not be namespaced."))
+    end
+    rhs_h[1] == namespace_hierarchy(nameof(lhs))[end] ||
+        throw(ArgumentError("LHS and RHS must have the same name."))
+
+    if !isequal(get_iv(lhs), get_iv(rhs))
+        throw(ArgumentError("LHS and RHS of replacement rule must have the same independent variable."))
+    end
+
+    lhs_u = get_unknowns(lhs)
+    rhs_u = Dict(get_unknowns(rhs) .=> nothing)
+    for u in lhs_u
+        if !haskey(rhs_u, u)
+            if isempty(namespace)
+                throw(ArgumentError("RHS of replacement rule does not contain unknown $u."))
+            else
+                throw(ArgumentError("Subsystem $(join([namespace; nameof(lhs)], NAMESPACE_SEPARATOR)) of RHS does not contain unknown $u."))
+            end
+        end
+        ru = getkey(rhs_u, u, nothing)
+        name = join([namespace; nameof(lhs); (hasname(u) ? getname(u) : Symbol(u))],
+            NAMESPACE_SEPARATOR)
+        l_connect = something(getconnect(u), Equality)
+        r_connect = something(getconnect(ru), Equality)
+        if l_connect != r_connect
+            throw(ArgumentError("Variable $(name) should have connection metadata $(l_connect),"))
+        end
+
+        l_input = isinput(u)
+        r_input = isinput(ru)
+        if l_input != r_input
+            throw(ArgumentError("Variable $name has differing causality. Marked as `input = $l_input` in LHS and `input = $r_input` in RHS."))
+        end
+        l_output = isoutput(u)
+        r_output = isoutput(ru)
+        if l_output != r_output
+            throw(ArgumentError("Variable $name has differing causality. Marked as `output = $l_output` in LHS and `output = $r_output` in RHS."))
+        end
+    end
+
+    lhs_p = get_ps(lhs)
+    rhs_p = Set(get_ps(rhs))
+    for p in lhs_p
+        if !(p in rhs_p)
+            if isempty(namespace)
+                throw(ArgumentError("RHS of replacement rule does not contain parameter $p"))
+            else
+                throw(ArgumentError("Subsystem $(join([namespace; nameof(lhs)], NAMESPACE_SEPARATOR)) of RHS does not contain parameter $p."))
+            end
+        end
+    end
+
+    lhs_s = get_systems(lhs)
+    rhs_s = Dict(nameof(s) => s for s in get_systems(rhs))
+
+    for s in lhs_s
+        if haskey(rhs_s, nameof(s))
+            rs = rhs_s[nameof(s)]
+            if isconnector(s)
+                name = join([namespace; nameof(lhs); nameof(s)], NAMESPACE_SEPARATOR)
+                if !isconnector(rs)
+                    throw(ArgumentError("Subsystem $name of RHS is not a connector."))
+                end
+                if (lct = get_connector_type(s)) !== (rct = get_connector_type(rs))
+                    throw(ArgumentError("Subsystem $name of RHS has connection type $rct but LHS has $lct."))
+                end
+            end
+            validate_replacement_rule(s => rs; namespace = [namespace; nameof(rhs)])
+            continue
+        end
+        name1 = join([namespace; nameof(lhs)], NAMESPACE_SEPARATOR)
+        throw(ArgumentError("$name1 of replacement rule does not contain subsystem $(nameof(s))."))
+    end
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Chain `getproperty` calls on `root` in the order given in `hierarchy`.
+
+# Keyword Arguments
+
+- `skip_namespace_first`: Whether to avoid namespacing in the first `getproperty` call.
+"""
+function recursive_getproperty(
+        root::AbstractSystem, hierarchy::Vector{Symbol}; skip_namespace_first = true)
+    cur = root
+    for (i, name) in enumerate(hierarchy)
+        cur = getproperty(cur, name; namespace = i > 1 || !skip_namespace_first)
+    end
+    return cur
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Recursively descend through `sys`, finding all connection equations and re-creating them
+using the names of the involved variables/systems and finding the required variables/
+systems in the hierarchy.
+"""
+function recreate_connections(sys::AbstractSystem)
+    eqs = map(get_eqs(sys)) do eq
+        eq.lhs isa Union{Connection, AnalysisPoint} || return eq
+        if eq.lhs isa Connection
+            oldargs = get_systems(eq.rhs)
+        else
+            ap::AnalysisPoint = eq.rhs
+            oldargs = [ap.input; ap.outputs]
+        end
+        newargs = map(get_systems(eq.rhs)) do arg
+            name = arg isa AbstractSystem ? nameof(arg) : getname(arg)
+            hierarchy = namespace_hierarchy(name)
+            return recursive_getproperty(sys, hierarchy)
+        end
+        if eq.lhs isa Connection
+            return eq.lhs ~ Connection(newargs)
+        else
+            return eq.lhs ~ AnalysisPoint(newargs[1], eq.rhs.name, newargs[2:end])
+        end
+    end
+    @set! sys.eqs = eqs
+    @set! sys.systems = map(recreate_connections, get_systems(sys))
+    return sys
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Given a hierarchical system `sys` and a rule `lhs => rhs`, replace the subsystem `lhs` in
+`sys` by `rhs`. The `lhs` must be the namespaced version of a subsystem of `sys` (e.g.
+obtained via `sys.inner.component`). The `rhs` must be valid as per the following
+conditions:
+
+1. `rhs` must not be namespaced.
+2. The name of `rhs` must be the same as the unnamespaced name of `lhs`.
+3. Neither one of `lhs` or `rhs` can be marked as complete.
+4. Both `lhs` and `rhs` must share the same independent variable.
+5. `rhs` must contain at least all of the unknowns and parameters present in
+   `lhs`.
+6. Corresponding unknowns in `rhs` must share the same connection and causality
+   (input/output) metadata as their counterparts in `lhs`.
+7. For each subsystem of `lhs`, there must be an identically named subsystem of `rhs`.
+   These two corresponding subsystems must satisfy conditions 3, 4, 5, 6, 7. If the
+   subsystem of `lhs` is a connector, the corresponding subsystem of `rhs` must also
+   be a connector of the same type.
+
+`sys` also cannot be marked as complete.
+"""
+function substitute_component(sys::T, rule::Pair{T, T}) where {T <: AbstractSystem}
+    iscomplete(sys) &&
+        throw(ArgumentError("Cannot replace subsystems of completed systems"))
+
+    validate_replacement_rule(rule)
+
+    lhs, rhs = rule
+    hierarchy = namespace_hierarchy(nameof(lhs))
+
+    newsys, _ = modify_nested_subsystem(sys, hierarchy) do inner
+        return rhs, ()
+    end
+    return recreate_connections(newsys)
+end

test/runtests.jl

@@ -98,6 +98,7 @@ end
             @safetestset "Causal Variables Connection Test" include("causal_variables_connection.jl")
             @safetestset "Debugging Test" include("debugging.jl")
             @safetestset "Namespacing test" include("namespacing.jl")
+            @safetestset "Subsystem replacement" include("substitute_component.jl")
         end
     end