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From Simone Tripodi <simonetrip...@apache.org>
Subject Re: [Graph] On graph weight type(s)
Date Fri, 23 Dec 2011 10:38:48 GMT
Hi Matthew!

I think that your idea is great as a foundation for implementing
algorithms but I would not allow users use that APIs to resolve known
problems, unless they want to implement their own solutions or
contribute back to [graph] missing algorithms.

Usually algorithms (like Dijkstra) already have clear enunciates and
steps are known, so we could safety expose 1 APIs that hide all that
details to clients wrapping your proposals.

WDYT? Thanks again!!!
-Simo

http://people.apache.org/~simonetripodi/
http://simonetripodi.livejournal.com/
http://twitter.com/simonetripodi
http://www.99soft.org/



On Fri, Dec 23, 2011 at 10:44 AM, Matthew Pocock
<turingatemyhamster@gmail.com> wrote:
> Hi Simo,
>
> I guess the 5 minutes to run example would be:
>
> ShortestPathFunction.dijkstra
>  .makeResult(graph, EdgeWeight.forWeightedEdge, Monotonic.sumDouble)
>  .findShortestPath(source, target);
>
> I was assuming that there would be standard pallets of all the strategies
> available statically in the obvious places. Actually, now I see the code
> written out in full like that, I'd perhaps consider renaming makeResult to
> `calculate` or `prepare` or some other verb.
>
> Matthew
>
> On 23 December 2011 08:47, Simone Tripodi <simonetripodi@apache.org> wrote:
>
>> Hi Matthew!
>>
>> at a first looks it is really interesting, just give me the time to
>> digest because at the same time I had the feeling of a little
>> over-engineering activity, I am worried that "5 minutes to run" users
>> would find it not so immediate.
>>
>> Thanks for providing stuff to learn from!
>> All the best,
>> -Simo
>>
>> http://people.apache.org/~simonetripodi/
>> http://simonetripodi.livejournal.com/
>> http://twitter.com/simonetripodi
>> http://www.99soft.org/
>>
>>
>>
>> On Thu, Dec 22, 2011 at 6:25 PM, Matthew Pocock
>> <turingatemyhamster@gmail.com> wrote:
>> > Hi,
>> >
>> > Just thought I'd throw something out here. My experience is that I often
>> > take the same graph (as in the exact same data, same objects) but at
>> > different times want to use different weights. So, rather than having
>> Edge
>> > extend Weighted<W>, I'd factor weights out into their own interface:
>> >
>> > /**
>> >  * An edge weight function.
>> >  *
>> >  * note: perhaps this should more generally just be a Function1<A, B>,
if
>> > we have such a thing handy.
>> >  *
>> >  * @tparam E  edge type
>> >  * @tparam W weight type
>> >  */
>> > public interface EdgeWeight<E, W> {
>> >  public W getWeight(E: Edge);
>> > }
>> >
>> > /**
>> >  * A combination of a monoid and comparator that satisfy monotinicity of
>> > the addition operation with respect to the comparator.
>> >  *
>> >  * ∀a: m.compare(m.zero, a) <= 0
>> >  * ∀a,b: m.compare(a, m.append(a, b)) <= 0
>> >  */
>> > public interface Monotonic<W> extends Monoid<W>, Comparator<W>
>> >
>> > Also, some algorithms calculate all shortest paths at once, while others
>> > calculate them individually and independently. It's probably even
>> possible
>> > to calculate some lazily. So, the interfaces for shortest paths should
>> > decouple setting up a strategy for all shortest paths from an object that
>> > can be used to fetch a specific shortest path.
>> >
>> > /**
>> >  * An algorithm for finding shortest paths between vertices of a graph,
>> > given some edge weighting function and
>> >  * a well-behaved combinator for edges between connected vertices.
>> >  */
>> > public interface ShortestPathFunction<V extends Vertex, E extends
>> Edge<E>,
>> > G extends DirectedGraph<V, E>, W> {
>> >  public ShortestPathResult<V, E, W> makeResult(G graph, EdgeWeight<E,
W>
>> > weighting, Monotonic<W> combineWith);
>> > }
>> >
>> > /**
>> >  * The shortest paths between vertices in a graph.
>> >  */
>> > public interface ShortestPathResult<V extends Vertex, E extends Edge<E>,
>> W>
>> > {
>> >  public WeightedPath<V, E, W> findShortestPath(V source, V target);
>> > }
>> >
>> > How does that look? You can then have standard implementations of these
>> > things in some static utility class or a spring-friendly resource. The
>> > brute-force algorithms that compute all paths at once would do all the
>> work
>> > in makeResult() and simply store this in some state within the returned
>> > ShortestPathResult. Those that calculate individual pairs on the fly (or
>> > all shortest paths from some vertex) would capture state in makeResult()
>> > and perform the actual computation in findShortestPath().
>> >
>> > Matthew
>> >
>> > On 22 December 2011 16:39, Claudio Squarcella <squarcel@dia.uniroma3.it
>> >wrote:
>> >
>> >> Hi,
>> >>
>> >>
>> >>  I highly appreciated the last contributions (thanks guys!) but I also
>> >>> agree on this point, so let's start from the end.
>> >>> I think that, no matter what underlying structure we come up with, the
>> >>> user should be able to specify e.g. a weighted edge with something like
>> >>>
>> >>> public class MyEdge implements Edge, Weighted<Double> { ... }
>> >>>
>> >>> and be able to immediately use it as an input for all the algorithms,
>> >>> without extra steps required. So the average user is happy, while
>> "graph
>> >>> geeks" can dig into advanced capabilities and forge their personalized
>> >>> weights :)
>> >>> I hope we all agree on this as a first step. Complexity comes after.
>> >>>
>> >>> I'll take my time as well to re-think.
>> >>>
>> >>
>> >> I did think and code a bit more. First of all please take a look at the
>> >> updated code: Weighted<W> is an interface (weight W can be any type)
and
>> >> all the algorithms require edges to implement Weighted<Double> for
now
>> --
>> >> we did not break it that much ;)
>> >>
>> >> About the "HasProperty-vs-Property" question (as in Comparable vs
>> >> Comparator, MonoidElement vs Monoid, etc) I would go for the second one
>> >> only. That is, external classes handle all operations on weights.
>> Downside:
>> >> the # of method parameters would increase linearly with the number of
>> >> properties, but I can live with that (how many properties would weights
>> >> have anyway?). On the other hand we have a neat interface for each
>> >> property/class (Zero, Semigroup, Monoid, Ordering or Comparator, etc)
>> and
>> >> one clean, generic implementation for each algorithm. Dijkstra's
>> signature
>> >> becomes something like:
>> >>
>> >> public static <V extends Vertex, W, WE extends WeightedEdge<W>,
G
>> extends
>> >> DirectedGraph<V, WE>> WeightedPath<V, WE, W> findShortestPath(
G graph,
>> V
>> >> source, V target, Monoid<W> weightMonoid, Comparator<W>
>> weightComparator )
>> >>
>> >> Scary uh? But wait, default implementations for Double, Integer, etc.
>> are
>> >> way easier. E.g. Dijkstra's shortcut for Double:
>> >>
>> >> public static <V extends Vertex, WE extends WeightedEdge<Double>,
G
>> >> extends DirectedGraph<V, WE>> WeightedPath<V, WE, Double>
>> findShortestPath(
>> >> G graph, V source, V target )
>> >> {
>> >>    return findShortestPath(graph, source, target, new DoubleMonoid(),
>> new
>> >> DoubleComparator());
>> >> }
>> >>
>> >> where DoubleMonoid and DoubleComparator are part of the library.
>> >>
>> >>
>> >> If you guys are fine with this, I'm ready to try and patch [graph] with
>> a
>> >> Christmas gift :)
>> >> Claudio
>> >>
>> >>
>> >> --
>> >> Claudio Squarcella
>> >> PhD student at Roma Tre University
>> >> E-mail address: squarcel@dia.uniroma3.it
>> >> Phone: +39-06-57333215
>> >> Fax: +39-06-57333612
>> >> http://www.dia.uniroma3.it/~**squarcel<
>> http://www.dia.uniroma3.it/~squarcel>
>> >>
>> >>
>> >>
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>> >>
>> >>
>> >
>> >
>> > --
>> > Dr Matthew Pocock
>> > Integrative Bioinformatics Group, School of Computing Science, Newcastle
>> > University
>> > mailto: turingatemyhamster@gmail.com
>> > gchat: turingatemyhamster@gmail.com
>> > msn: matthew_pocock@yahoo.co.uk
>> > irc.freenode.net: drdozer
>> > skype: matthew.pocock
>> > tel: (0191) 2566550
>> > mob: +447535664143
>>
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>> To unsubscribe, e-mail: dev-unsubscribe@commons.apache.org
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>>
>>
>
>
> --
> Dr Matthew Pocock
> Integrative Bioinformatics Group, School of Computing Science, Newcastle
> University
> mailto: turingatemyhamster@gmail.com
> gchat: turingatemyhamster@gmail.com
> msn: matthew_pocock@yahoo.co.uk
> irc.freenode.net: drdozer
> skype: matthew.pocock
> tel: (0191) 2566550
> mob: +447535664143

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