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

[Kish Shen]

Hi,

I am still trying to figure out how to add restart based search to 
ECLiPSe's interface to Gecode. I tried modifying my existing code (which 
does not support restart-based search), and managed to get a restarted 
based bab search to return the optimal answer, but the code then 
crashes, probably because I am not doing things correctly.

If someone can point me in the right direction, I would be very 
grateful. I sent a message about this about 2 weeks ago to this mailing 
list, but perhaps I did not give the correct information to get any 
help, so I will try again.

An outline of what I am doing now:

The user defines the problem to be solved in ECLiPSe, and the interface 
maps this to Gecode. At the Gecode level, the problem is represented in
GecodeSpace, which is derived from Gecode::MinimizeSpace

Searching can be done with a Gecode search engine, or it can be done at 
the ECLiPSe level (in which case search engines are not used).

To do the search with a search engine, I have a GecodeSearch class,
which has a Search::Engine* sengine, which is then dynamically assigned 
with the problem and search engine type when the user specify that a 
search is to be done by Gecode with a particular search method (like 
bab), e.g.

solver->vCost = <Cost variable>
sengine = Search::bab(solver, option)

where solver is a GecodeSpace*, and vCost is the cost variable (for 
MinimizeSpace).

The MPG describes the search engine classes such as BAB, which I don't 
use directly. I think the reason is that I want to be able to assign 
different types of search engines to sengine, as the search type is only 
known at run-time, and in fact the user can call search as often as they 
like on the same problem.

My problem is that I cannot extend this current scheme to work with 
restart-based search. What I tried was to use Search::rbs, which is also 
of class Engine*, and so can be assigned to sengine, but this crashed 
after returning the solution:

sengine0 = Search::bab(solver, option);
sengine = Search::rbs(solver, metastop, sengine0, metaoption);

I needed to use an extra Engine* sengine0, because using the same engine 
in bab and rbs crashed immediately.

The crash seems to happen when the rbs engine is destroyed, and it looks 
like it is related to using 2 search engines.

Is rbs supposed to be used by the user? I found it by looking for rbs in 
the documentation, but I noticed that although it is listed, it doesn't 
seem to have any description associated with it.

Can I use Engine* in this way if I want to use restart-based search, or 
do I need to use something else (i.e. not a Engine*)?

Thanks in advance for any help!

Cheers,

Kish