Keep invview for var_matching valid in pss

Previously we could introduce inconsistent assignments, which caused
the invview to be wrong after the return from pss.

Author: Keno

src/bipartite_graph.jl

@@ -63,7 +63,10 @@ end
 function Base.setindex!(m::Matching{U}, v::Union{Integer, U}, i::Integer) where {U}
     if m.inv_match !== nothing
         oldv = m.match[i]
-        isa(oldv, Int) && (m.inv_match[oldv] = unassigned)
+        if isa(oldv, Int)
+            @assert m.inv_match[oldv] == i
+            m.inv_match[oldv] = unassigned
+        end
         isa(v, Int) && (m.inv_match[v] = i)
     end
     return m.match[i] = v

src/structural_transformation/partial_state_selection.jl

@@ -86,6 +86,9 @@ function pss_graph_modia!(structure::SystemStructure, var_eq_matching, varlevel,
             filter!(eq -> invview(ict.graph.matching)[eq] === unassigned, to_tear_eqs)
             tearEquations!(ict, solvable_graph.fadjlist, to_tear_eqs, BitSet(to_tear_vars),
                            nothing)
+            for var in to_tear_vars
+                var_eq_matching[var] = unassigned
+            end
             for var in to_tear_vars
                 var_eq_matching[var] = ict.graph.matching[var]
             end