[gecode-users] Not all solutions, BAB vs. DFS

[Guido Tack]

Martin Kreißig wrote:

> Hello,
>
> I found out, that GECODe is a very good (if not the best) solution  
> to my problem.
> The thing is, that I never used C++ before - everybody has to start  
> at a point ;)
>
> So far I got used to it, but now - when finished - I don't get all  
> solutions of my problem.
>
> Searching in this list I found out that I have to use the BAB search  
> and add the option opt.solutions(0)...

You can use opt.solutions(0) with DFS, too.

> The program worked with DFS before.
> But now I get the error:
> 	"terminate called after throwing an instance of  
> 'Gecode::SpaceConstrainUndefined' what(): Space::constrain: Attempt  
> to use undefined constrain function"

BAB is for solving optimization problems, and requires implementing  
the constrain function.  If you don't want to do optimization, use DFS.

> My implementation does not follow the syntax given in the examples,  
> like:
> 	"Script::run<Money,DFS,Options>(opt);"
>
> I am starting the search by this:
> 	DFS<CSP> dfs( csp_obj );
>
> So my question is - maybe a bit of a beginner one - this is not  
> possible
> with BAB?
>
> How can I add the options variable in this implementation? BAB<CSP>
> dfs( csp_obj, opt ); is not working.

The dfs object has a next method that you can call in a loop to get  
more than one solution.  As soon as it returns NULL, the complete  
search tree has been explored:

CSP* c = dfs.next();
while (c != NULL) {
	c->print(); // e.g., output the current solution
	delete c;
	c = dfs.next();
}

Cheers,
	Guido