[Lemon-user] Question about copying graphs and maps

[Dalia De Santis]

Hi Alpár,

thank you for your kind answer.
There was definitely a bug in here, as you pointed out!
>It looks like a bug. I think 'nodes' and 'arches' should be attached to
>g, not to _g


>First of all, are you sure you really want to copy it? If you need it
>because you want the work with slightly modified versions of a base
>graph, then you might also consider using SubDigraph adaptor and/or
>custom map adaptors.
Actually you are right. There might be no need to copy an entire graph as I
want to keep references.
I'll have a broader look into SubDigraph and custom adaptors and try to use
them in a smart way.

Thank you for your help!

Dalia


2012/7/29 Alpár Jüttner <alpar at cs.elte.hu>

> Hi,
>
> > I am very new to Lemon and I am a bit confused about graph copying.
>
> First of all, are you sure you really want to copy it? If you need it
> because you want the work with slightly modified versions of a base
> graph, then you might also consider using SubDigraph adaptor and/or
> custom map adaptors.
>
> > I have to copy a graph and some related maps in a constructor of my
> > class:
> >
> > class network_map
> >     {
> >     public:
> >         ListDigraph g;
> >         ListDigraph::NodeMap<node_block>  nodes;
> >         ListDigraph::ArcMap<arc_block>    arches;
> >
> >         network_map  (const ListDigraph & _g,
> >                               const ListDigraph::NodeMap<node_block>
> > & _nm,
> >                               const ListDigraph::ArcMap<arc_block> &
> > _am)
> >                             : g(), nodes(_g), arches(_g)
>
> It looks like a bug. I think 'nodes' and 'arches' should be attached to
> g, not to _g:
>
> : g(), nodes(g), arches(g)
>
> >         {
> >             DigraphCopy<ListDigraph,ListDigraph> dg_copy(_g,g);
> >
> >             // create nodes and arches references: is it necessary?
> >             ListDigraph::NodeMap<node_block> nmap(g);
> >             ListDigraph::ArcMap<arc_block> amap(g);
> >             dg_copy.nodeRef(nmap);
> >             dg_copy.arcRef(amap);
> >
> >             // copy maps:
> >             dg_copy.nodeMap(_nm,nodes);
> >             dg_copy.arcMap(_am, arches);
> >
> >             dg_copy.run();
> >         };
> >    };
> >
> > The maps of nodes and arches "nm" and "am" refers to the graph _g that
> > I want to copy. My class maps are created to refer to the class graph
> > g that will be a copy of the input graph _g, and they will be in turn
> > a copy on n, and am.
> >  I want to be sure that my new graph g contains all references to _g,
> > as I want to use it in my class as it were _g.
>
> The (cross)references are used to map the original and the copied
> node/arcs to each other.
>
> In your example if _n is a node of _g, then the corresponding node in g
> is nmap[n].
>
> > My questions are:
> > - Is it necessary to copy node references from a convenience map
> > (nmap) of the original graph if I am copying a map that already refers
> > to the original graph nodes?
>
> Not sure if I understand your question correctly, but you don't have to
> use .nodeRef()/.arcRef() explicitely if you don't need values.
>
> Note however that DigraphCopy will create temporary ones internally
> anyway.
>
> > - What does .nodeRef(map) exactly do?
>
> See above.
>
> Note that you can also use digraphCopy(), which might be simpler.
>
>         digraphCopy(g,_g).nodeMap(_nm,nodes).arcMap(_am,arcs).run();
>
> Regards,
> Alpar
>
> > I hope this is clear to you!
> > Thank you in advance,
> >
> > --
> > Dalia De Santis
> >
> > MEng, Ph.D. Student
> > Istituto Italiano di Tecnologia
> > Robotics, Brain and Cognitive Sciences Dept.
> > Via Morego, 30, 16163 Genova
> > dalia.desantis at iit.it
> >
> >
> > _______________________________________________
> > Lemon-user mailing list
> > Lemon-user at lemon.cs.elte.hu
> > http://lemon.cs.elte.hu/mailman/listinfo/lemon-user
>
>
>
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