The S-representation of a graph is a list of (vertex-neighbours) pairs,
where the pairs are in standard order (as produced by keysort) and the
neighbours of each vertex are also in standard order (as produced by
sort). This form is convenient for many calculations.
A new UGraph from raw data can be created using
vertices_edges_to_ugraph/3.
Adapted to support some of the functionality of the SICStus ugraphs
library by Vitor Santos Costa.
Ported from YAP 5.0.1 to SWI-Prolog by Jan Wielemaker.
- author
- - R.A.O'Keefe
- - Vitor Santos Costa
- - Jan Wielemaker
- license
- - GPL+SWI-exception or Artistic 2.0
- vertices(+S_Graph, -Vertices) is det
- Strips off the neighbours lists of an S-representation to
produce a list of the vertices of the graph. (It is a
characteristic of S-representations that every vertex appears,
even if it has no neighbours.). Vertices is in the standard
order of terms.
- vertices_edges_to_ugraph(+Vertices, +Edges, -UGraph) is det
- Create a UGraph from Vertices and edges. Given a graph with a
set of Vertices and a set of Edges, Graph must unify with the
corresponding S-representation. Note that the vertices without
edges will appear in Vertices but not in Edges. Moreover, it is
sufficient for a vertice to appear in Edges.
?- vertices_edges_to_ugraph([],[1-3,2-4,4-5,1-5], L).
L = [1-[3,5], 2-[4], 3-[], 4-[5], 5-[]]
In this case all vertices are defined implicitly. The next
example shows three unconnected vertices:
?- vertices_edges_to_ugraph([6,7,8],[1-3,2-4,4-5,1-5], L).
L = [1-[3,5], 2-[4], 3-[], 4-[5], 5-[], 6-[], 7-[], 8-[]]
- del_vertices(+Graph, +Vertices, -NewGraph) is det
- Unify NewGraph with a new graph obtained by deleting the list of
Vertices and all the edges that start from or go to a vertex in
Vertices to the Graph. Example:
?- del_vertices([1-[3,5],2-[4],3-[],4-[5],5-[],6-[],7-[2,6],8-[]],
[2,1],
NL).
NL = [3-[],4-[5],5-[],6-[],7-[6],8-[]]
- Compatibility
- - Upto 5.6.48 the argument order was (+Vertices, +Graph,
-NewGraph). Both YAP and SWI-Prolog have changed the argument
order for compatibility with recent SICStus as well as
consistency with del_edges/3.
- ugraph_union(+Set1, +Set2, ?Union)
- Is true when Union is the union of Set1 and Set2. This code is a
copy of set union
- edges(+UGraph, -Edges) is det
- Edges is the set of edges in UGraph. Each edge is represented as
a pair From-To, where From and To are vertices in the graph.
- transpose_ugraph(Graph, NewGraph) is det
- Unify NewGraph with a new graph obtained from Graph by replacing
all edges of the form V1-V2 by edges of the form V2-V1. The cost
is O(|V|*log(|V|)). Notice that an undirected graph is its own
transpose. Example:
?- transpose([1-[3,5],2-[4],3-[],4-[5],
5-[],6-[],7-[],8-[]], NL).
NL = [1-[],2-[],3-[1],4-[2],5-[1,4],6-[],7-[],8-[]]
- Compatibility
- - This predicate used to be known as transpose/2.
Following SICStus 4, we reserve transpose/2 for matrix
transposition and renamed ugraph transposition to
transpose_ugraph/2.
- compose(G1, G2, Composition)
- Calculates the composition of two S-form graphs, which need not
have the same set of vertices.
- top_sort(+Graph, -Sorted) is semidet
- top_sort(+Graph, -Sorted, ?Tail) is semidet
- Sorted is a topological sorted list of nodes in Graph. A
toplogical sort is possible if the graph is connected and
acyclic. In the example we show how topological sorting works
for a linear graph:
?- top_sort([1-[2], 2-[3], 3-[]], L).
L = [1, 2, 3]
The predicate top_sort/3 is a difference list version of
top_sort/2.
- neighbors(+Vertex, +Graph, -Neigbours) is det
- neighbours(+Vertex, +Graph, -Neigbours) is det
- Neigbours is a sorted list of the neighbours of Vertex in Graph.
- connect_ugraph(+UGraphIn, -Start, -UGraphOut) is det
- Adds Start as an additional vertex that is connected to all vertices
in UGraphIn. This can be used to create an topological sort for a
not connected graph. Start is before any vertex in UGraphIn in the
standard order of terms. No vertex in UGraphIn can be a variable.
Can be used to order a not-connected graph as follows:
top_sort_unconnected(Graph, Vertices) :-
( top_sort(Graph, Vertices)
-> true
; connect_ugraph(Graph, Start, Connected),
top_sort(Connected, Ordered0),
Ordered0 = [Start|Vertices]
).
- complement(+UGraphIn, -UGraphOut)
- UGraphOut is a ugraph with an edge between all vertices that are
not connected in UGraphIn and all edges from UGraphIn removed.
- To be done
- - Simple two-step algorithm. You could be smarter, I suppose.
- reachable(+Vertex, +UGraph, -Vertices)
- True when Vertices is an ordered set of vertices reachable in
UGraph, including Vertex.
Undocumented predicates
The following predicates are exported, but not or incorrectly documented.
- transitive_closure(Arg1, Arg2)
- del_edges(Arg1, Arg2, Arg3)
- add_edges(Arg1, Arg2, Arg3)
- add_vertices(Arg1, Arg2, Arg3)