(*
* Acyclic subgraph adaptor. This takes a linear order of node id
* return a view in which only the edges (and nodes) consistent with
* the linear order is visible.
*
* -- Allen
*)
signature ACYCLIC_SUBGRAPH_VIEW =
sig
(* Acyclic node induced subgraph *)
val acyclic_view : Graph.node_id list ->
('n,'e,'g) Graph.graph ->
('n,'e,'g) Graph.graph
end
structure AcyclicSubgraphView : ACYCLIC_SUBGRAPH_VIEW =
struct
structure G = Graph
structure A = HashArray
structure S = Subgraph_P_View
fun acyclic_view nodes (G as G.GRAPH g) =
let val ord = A.array(#capacity g (),~1)
fun order(i,[]) = ()
| order(i,n::ns) = (A.update(ord,n,i); order(i+1,ns))
val _ = order(0,nodes)
fun node_p i = A.sub(ord,i) >= 0
fun edge_p (i,j) =
let val i = A.sub(ord,i)
in i >= 0 andalso i < A.sub(ord,j) end
in S.subgraph_p_view nodes node_p edge_p G
end
end