Re: Recursion and how to construct a graph? (What is the boundary condition?)

Hi Ben

take a look at library(ugraph), specifically
vertices_edges_to_ugraph<http://www.swi-prolog.org/pldoc/doc_for?object=vertices_edges_to_ugraph/3>
.

I have a loosely related note: you graph is already 'built', just in an
alternative format.
Which format to prefer depends from the task: for instance RDF more
resembles the edge/2 representation than a list.


bye Carlo


2013/8/30 Ben Engbers <[email protected]>

> I have found lots of examples on how to construct a path through a
> graph, but I didn't find any examples on how to construct the graph
> itselfand that's exactly what I need to do..
>
> I have a set of edges, all in the form edge( from, to, value) and I want
> to construct a graph (list) for which 'from' is member.
> Length(Graph) has to be >2.
>
> In pseudocode I wanted to do this:
>
> construct_graph( X, Graph) :-
>   If \+member(X, Graph) Then construct_graph(X, [X|Graph]). /* Add X to
> the graph, Recursion */
>
> construct_graph( X, Graph) :-
>    edge( X, To, Value), construct_graph( To, Graph), /* all the edges
> for which X is starting point
>    edge( To, X, Value), construct_graph( To, Graph). /* all the edges
> for which X is end point
>
> construct_graph( X, Graph) :-
>    \+edge( X, _, _). /* X is not starting point for other edges.
>
>
> In all the examples that I see for recursion, the ending boundary
> condition is the first clause.
> In my pseudocode, the ending boundary condition is the last clause.
>
> My question is if this approach will work?
>
> Ben Engbers
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