Fix input type for is_chordal

Originally, we restricted the input type for is_chordal to AbstractSimpleGraph to rule out parallel edges, but some other graph types we would like to support (such as SimpleWeightedGraph) are of the more general AbstractGraph type. It turns out the current AbstractGraph interface aleady does not support parallel edges, so there is no worry here--it is already stated in the Implementation Notes anyway that is_chordal should not take in graphs with parallel edges as input.

Author: Luis-Varona

src/chordality.jl

@@ -34,8 +34,8 @@ parallel edges.
 # Examples
 TODO: Add examples
 """
-function is_chordal(g::AbstractSimpleGraph)
-    # The possibility of self-loops is already ruled out by the `AbstractSimpleGraph` type
+function is_chordal(g::AbstractGraph)
+    # The `AbstractGraph` interface does not support parallel edges, so no need to check
     is_directed(g) && throw(ArgumentError("Graph must be undirected"))
     has_self_loops(g) && throw(ArgumentError("Graph must not have self-loops"))
 
@@ -69,10 +69,10 @@ function is_chordal(g::AbstractSimpleGraph)
 end
 
 function _max_cardinality_node(
-    g::AbstractSimpleGraph, unnumbered::Set{T}, numbered::Set{T}
+    g::AbstractGraph, unnumbered::Set{T}, numbered::Set{T}
 ) where {T}
     cardinality(v::T) = count(in(numbered), neighbors(g, v))
     return argmax(cardinality, unnumbered)
 end
 
-_is_complete_graph(g::AbstractSimpleGraph) = density(g) == 1
+_is_complete_graph(g::AbstractGraph) = density(g) == 1