[gecode-users] Adding restart-based search to ECLiPSe's interface to Gecode

[Christian Schulte]

What I wrote earlier was just nonsense. I think I really have to use my
brain here and think it through how to do it best. I'll get back to you
later.

Christian

--
Christian Schulte, www.ict.kth.se/~cschulte


-----Original Message-----
From: Kish Shen [mailto:kisshen at cisco.com] 
Sent: Friday, August 23, 2013 08:26 PM
To: cschulte at kth.se
Cc: users at gecode.org
Subject: Re: [gecode-users] Adding restart-based search to ECLiPSe's
interface to Gecode

Hi Christian,

Thanks for your reply again!

I am reluctant to use Gecode features that are not in the official releases
yet, as the user should be able to compile ECLiPSe and its open-source
third-party components (like Gecode) on their own.

Currently, the released gfd interface is to Gecode 3.7. I have not updated
the release to Gecode 4(.2) mainly because I do not want to remove the
RESTART search engine, only to reintroduce the equivalent when I get RBS
working with gfd.

I understand that it is easiest and perhaps best to use a common base type
for the search engines, but in the absence of this base type at the moment,
should I try to hide the different types of search engines inside my
GecodeSearch class? Currently I have a singe Engine* (sengine) that points
to the actual search engine, and a next method to obtain the next solution
but I assume I can have different (private) pointers to the different search
engines, and a next method that calls the appropriate next, depending on the
search method.

I also have a related question about getting the next solution with RBS
-- I had assumed that the next solution will be computed with a restart, but
as there seems to be 2 search engines in rbs, with RBS controlling the
restart on another engine doing the "actual" search (e.g. BAB), I am
wondering if the behaviour when getting the next solution is controlled by
this "actual" search engine, and for BAB, I don't think this is done with a
restart (hence the need for the old RESTART engine). So is the search
restarted when next() is called in RBS, or does this depend on the "actual"
search engine?

Assuming that the search is restarted with next(), then can the
functionality of the old RESTART engine be reproduced by setting the cutoff
threshold to be very high? A related question is if it make sense (and if
so, is there any way to do so) to use something other than the number of
failures for deciding when to restart?

Cheers,
Kish


On 22/08/2013 08:49, Christian Schulte wrote:
> Hi Kish,
>
> My bad... There is really no common basetype for search engines, the 
> type I mentioned is actually for the implementations and not the
interfaces...
>
> I think you will have to wait until I have added a common basetype 
> (there is a basetype, but it is not powerful enough), I might be able 
> to do it until the end of the week.
>
> Sorry for the confusion!
>
> Cheers
> Christian
>
> --
> Christian Schulte, Professor of Computer Science, KTH, 
> www.ict.kth.se/~cschulte/
>
>
>
> -----Original Message-----
> From: Kish Shen [mailto:kisshen at cisco.com]
> Sent: Thursday, August 22, 2013 9:45 AM
> To: cschulte at kth.se
> Cc: users at gecode.org
> Subject: Re: [gecode-users] Adding restart-based search to ECLiPSe's 
> interface to Gecode
>
> Hi Christian,
>
> Thanks again!
>
> On 21/08/2013 19:17, Christian Schulte wrote:
>> Try to avoid the Gecode::Search::bab .... functions. Just create as
> follows:
>> 	Gecode::Search::Engine* e = new Gecode::BAB(...) Then it also will 
>> work for RBS, and you do not have to create a second engine yourself, 
>> this will the RBS class do for you.
>>
>> And do not forget to delete e eventually!
>>
>
> This is the part that I don't know how to do correct -- probably 
> because of my lack of C++ knowledge, but as far as I can tell, 
> Gecode::DFS etc are not of class Engine*, according to the doc:
>
> template<class T>
> class Gecode::DFS<T>
>
> for subclasses T of Space
>
> T is GecodeSpace in my case, I assume. I am not sure what class DFS 
> is, but I can't see how it could be Engine*.
>
> Anway, I tried to do the assignment as you suggested:
>
>
> Search::Engine* segine;
> ...
> sengine = new DFS<GecodeSpace>(solver, o); and indeed I get the error
>
> cannot convert 'Gecode::DFS<GecodeSpace>*' to 'Gecode::Search::Engine*'
>
> (I first tried sengine = new DFS(solver, o) but got an error 'expected
> type-specifier')
>
> So I am not sure what to do -- do I need to change the type of 
> sengine, and/or the way I assign an engine to sengine?
>
> Cheers,
>
> Kish
>
>
>
>