Topsort observed equations

Author: YingboMa

docs/src/tutorials/acausal_components.md

@@ -406,10 +406,15 @@ observed(sys)
  capacitor₊n₊v(t) ~ 0.0
  source₊n₊v(t) ~ 0.0
  ground₊g₊i(t) ~ 0.0
- ⋮
+ source₊n₊i(t) ~ capacitor₊p₊i(t)
+ source₊p₊i(t) ~ -capacitor₊p₊i(t)
+ capacitor₊n₊i(t) ~ -capacitor₊p₊i(t)
+ resistor₊n₊i(t) ~ -capacitor₊p₊i(t)
  ground₊g₊v(t) ~ 0.0
  source₊p₊v(t) ~ source₊V
  capacitor₊p₊v(t) ~ capacitor₊v(t)
+ resistor₊p₊v(t) ~ source₊p₊v(t)
+ resistor₊n₊v(t) ~ capacitor₊p₊v(t)
  resistor₊v(t) ~ -((capacitor₊p₊v(t)) - (source₊p₊v(t)))
 ```
 

src/systems/abstractsystem.jl

@@ -467,6 +467,13 @@ end
 """
 $(SIGNATURES)
 
-Structurally simplify algebraic equations in a system.
+Structurally simplify algebraic equations in a system and compute the
+topological sort of the observed equations.
 """
-structural_simplify(sys::AbstractSystem) = tearing(alias_elimination(sys))
+function structural_simplify(sys::AbstractSystem)
+    ss = states(sys)
+    sys = tearing(alias_elimination(sys))
+    s = structure(sys)
+    @set! sys.observed = topsort_equations(observed(sys), ss)
+    return sys
+end

src/systems/diffeqs/odesystem.jl

@@ -235,7 +235,7 @@ ODESystem(eq::Equation, args...; kwargs...) = ODESystem([eq], args...; kwargs...
 $(SIGNATURES)
 
 Build the observed function assuming the observed equations are all explicit,
-i.e. there are no cycles or dependencies.
+i.e. there are no cycles.
 """
 function build_explicit_observed_function(
         sys, syms;