Re: library(ugraphs)

On 02/13/2014 10:57 AM, Nicos Angelopoulos wrote:
>
>
> Dear all,
>
> 1.
>	library(ugraphs)  seems to have lost documentation for a number of its predicates-
>	http://www.swi-prolog.org/pldoc/doc/swi/library/ugraphs.pl
>	probably due to a very recent change as my local spuds server had full documentation
>	until the last update from pl-devel

This is a common issue with libraries that are partially documented in
the source, but for which the `official' documentation is still in
LaTeX. The complete docs are in
http://www.swi-prolog.org/pldoc/man?section=ugraphs. The long term
solution is to move the docs to the source and generate the LaTeX from
there as is done for quite a few libraries, notably the ones under more
active development.

If anyone likes to help, submit patches that move the documentation from
the LaTeX source into the library.

> 2.
>	i am not sure if this is of general enough interest to be included in the library,
>	but i recently coded a sub_graphs/2 predicate
>	this includes a use case for the ord_select/3 predicate discussed previously

Richard often has good remarks about such issues ...

	Cheers --- Jan

>
>
> Regards,
>
> Nicos Angelopoulos
> ---
> http://stoics.org.uk/~nicos/
>
>
> :- requires(ord_select/3).
>
> %% sub_graphs(+Graph, -Subs).
> %
> % Subs is all disconnected subgraphs in Graph
> %
> % ==
> % sub_graphs([1-[2,3],2-[3],3-[4],4-[],5-[6,7],6-[],7-[6]], Subs).
> %
> % Subs = [[1-[2, 3], 2-[3], 3-[4], 4-[]], [5-[6, 7], 6-[], 7-[6]]].
> % ==
> %
> % @author nicos angelopoulos
> % @version 0.1  2014/02/12
> %
> sub_graphs([], []).
> sub_graphs(Graph, [Removed|TSubs]) :-
>	\+ var(Graph),                            % can be moved to an outer wrapper, or removed
>	Graph = [Vertex-_|_],
>	reachable(Vertex, Graph, Vertices),
>	select_vertex_entries(Graph, Vertices, Removed, Reduced),
>	sub_graphs(Reduced, TSubs).
>
> %% del_vertex_entries(+Graph, +Vertices, -Removed, -Reduced).
> %
> %  Delete the entries for a set of Vertices from Graph.
> %  This differs from del_vertices/3, in that it does not remove edges and also
> %  returns what was removed.  The main use case for this predicate,
> %  is for when we are removing whole isolated sub graphs.
> %  It probably best, it should be kept away from library interfaces.
> %  This version fails if one of the Vertices is not in Graph.
> %
> %  @author nicos angelopoulos
> %  @version 0.1  2014/02/12
> %
> select_vertex_entries([], [], [], []).                        % test 2nd arg if you want to throw error.
> select_vertex_entries([V-Edged|T], Vertices, Removed, Reduced) :-
>	ord_select(Vertices, V, RemVertices),
>	!,
>	Removed = [V-Edged|TRemoved],
>	select_vertex_entries(T, RemVertices, TRemoved, Reduced).
> select_vertex_entries([V-Edged|T], Vertices, Removed, [V-Edged|TReduced]) :-
>	select_vertex_entries(T, Vertices, Removed, TReduced).
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