[gecode-users] Consecutive instances of Gecode produce different results

[Pascal Francq (Mailing lists)]

After several tests, it seems in fact that it is a rounding issue :
several combinations of the parameters give an identical result if
printed. I will check further if there is no bug in my code, but it
seems that is not a Gecode problem.
Thanks.

Le 28/05/13 22:47, Christian Schulte a écrit :
> Yes, that was also my suspicion: maybe it is a rounding issue.
> 
>  
> 
> Best
> 
> Christian
> 
>  
> 
> --
> 
> Christian Schulte, www.ict.kth.se/~cschulte/
> 
>  
> 
> *From:*users-bounces at gecode.org [mailto:users-bounces at gecode.org] *On
> Behalf Of *Guido Tack
> *Sent:* Tuesday, May 28, 2013 10:45 PM
> *To:* Pascal Francq
> *Cc:* users at gecode.org
> *Subject:* Re: [gecode-users] Consecutive instances of Gecode produce
> different results
> 
>  
> 
> The propagator looks ok (waiting for all variables to be assigned is
> definitely monotonic). I think I'd add some debugging output to your
> propagate function, printing the v and l arrays and the resulting Cost
> whenever it is computed successfully.  Perhaps that at least gives you
> an idea if the integer variables are already different or if it's the
> floating point computation.
> 
>  
> 
> Cheers,
> 
> Guido
> 
>  
> 
> -- 
> 
> Guido Tack
> 
> http://www.csse.monash.edu/~guidot/
> 
>  
> 
>  
> 
>  
> 
> On 24/05/2013, at 6:51 AM, Pascal Francq (Mailing lists)
> <mailing-list at francq.info <mailto:mailing-list at francq.info>> wrote:
> 
> 
> 
> 1. My propagator is very simple : It waits until all v and I are
> assigned. Then, it computes a cost function (to optimize) depending from
> these variables.
> 
> 
> //-----------------------------------------------------------------------------
> PropCost RChoquetPropagator::cost(const Space&, const ModEventDelta&) const
> {
>           return PropCost::binary(PropCost::HI);
> }
> 
> //-----------------------------------------------------------------------------
> ExecStatus RChoquetPropagator::propagate(Space& home, const ModEventDelta&)
> {
>           if((!v.assigned())||(!I.assigned()))
>                       return (ES_NOFIX);
>           double Res(Compute(*this)); // Make some computation
>           if(Res<-1.0||Res>1.0)
>                       throw std::range_error("Cost function must be in
> [-1,1]");
>           if(Cost.eq(home,Res)==Float::ME_FLOAT_FAILED)
>                       return ES_FAILED;
>           return home.ES_SUBSUMED(*this);
> }
> 
> 2. I don't have program any parallel searches.
> 
> I will check 22.9 in MPG (for the moment, I relaunch the program several
> times rather than calling a function multiple times in the same program
> run).
> 
> Le 23/05/13 21:27, Christian Schulte a écrit :
> 
> Oh, I see. That means that there is most likely a bug (could also be ok) in
> your own propagator.
> 
> Normally, a propagator must be monotonic: it never propagates more when it
> is run on bigger variables domains. Or with other words: the smaller the
> domains the more it propagates.
> 
> Some propagation algorithms do not follow this which might lead to
> indeterminstic behavior as you observed. Check 22.9 in MPG.
> 
> But most likely it is a bug in your propagator.
> 
> Or do you use parallel search with several threads? This can also lead to
> non-deterministic behavior.
> 
> Cheers
> Christian
> 
> --
> Christian Schulte, www.ict.kth.se/~cschulte/
> <http://www.ict.kth.se/~cschulte/>
> 
> 
> 
> -----Original Message-----
> From: Pascal Francq (Mailing lists) [mailto:mailing-list at francq.info
> <mailto:list at francq.info>]
> Sent: Thursday, May 23, 2013 5:43 PM
> To: cschulte at kth.se <mailto:cschulte at kth.se>
> Subject: Re: [gecode-users] Consecutive instances of Gecode produce
> 
> different
> 
> results
> 
> I use two Gecode::IntVarArray variables I and v. The code for the
> 
> constraints and
> 
> the branching is the following one :
> 
> // Maximal value <= 1
> rel(*this,1>=sum(v));
> 
> // Sum_(i)(2*v[i]-Sum_(j,j<>i)(I[i,j])>=0
> for(size_t i=0;i<4;i++)
> {
>   IntVar tmp[3];
>   size_t idx(0);
>   for(size_t j=0;j<4;j++)
>   {
>      if(i==j)
>         continue;
>      if(idx)
>         tmp[idx]=expr(*this,tmp[idx-1]-abs(I[i,j]));
>      else
>         tmp[idx]=expr(*this,-abs(I[i,j]));
>      idx++;
>    }
>    rel(*this, 0<=2*v[i]+tmp[idx-1]);
> }
> 
> // Call my own propagator
> choquetPropagator(*this,Test,v,I,Cost);
> 
> // Make the branch
> branch(*this,v,INT_VAR_SIZE_MIN(),INT_VAL_MIN());
> branch(*this,I,INT_VAR_SIZE_MIN(),INT_VAL_MIN());
> 
> 
> Le 23/05/13 17:23, Christian Schulte a écrit :
> 
> Could you tell us which constraints and which branchings you are using?
> 
> Best
> Christian
> 
> --
> Christian Schulte, Professor of Computer Science, KTH,
> www.ict.kth.se/~cschulte/ <http://www.ict.kth.se/~cschulte/>
> 
> 
> -----Original Message-----
> From: users-bounces at gecode.org <mailto:users-bounces at gecode.org>
> [mailto:users-bounces at gecode.org] On
> Behalf Of Pascal Francq (Mailing lists)
> Sent: Thursday, May 23, 2013 4:59 PM
> To: users at gecode.org <mailto:users at gecode.org>
> Subject: [gecode-users] Consecutive instances of Gecode produce
> different results
> 
> Hi,
> I have a strange problem : I have a function that runs a Gecode
> instance for a particular problem. When I call the function several
> times, the result of the first run sometimes differs from those of the
> 
> other
> 
> ones.
> 
> I have make some runs with valgrind, but I see nothing. Has anyone an
> idea where to search ?
> --
> Dr. Pascal Francq
> Belgium
> 
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> 
> 
> 
> --
> Dr. Pascal Francq
> Belgium
> 
>  
> 
> 
> 
> -- 
> Dr. Pascal Francq
> Belgium
> 
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>  
> 


-- 
Dr. Pascal Francq
Belgium