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

[Guido Tack]

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> 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/
>> 
>> 
>>> -----Original Message-----
>>> From: Pascal Francq (Mailing lists) [mailto:mailing-list at francq.info]
>>> Sent: Thursday, May 23, 2013 5:43 PM
>>> To: 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/
>>>> 
>>>> 
>>>> -----Original Message-----
>>>> From: 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
>>>> 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
>>>> 
>>>> _______________________________________________
>>>> Gecode users mailing list
>>>> users at gecode.org
>>>> https://www.gecode.org/mailman/listinfo/gecode-users
>>>> 
>>> 
>>> 
>>> --
>>> Dr. Pascal Francq
>>> Belgium
>> 
> 
> 
> -- 
> Dr. Pascal Francq
> Belgium
> 
> _______________________________________________
> Gecode users mailing list
> users at gecode.org
> https://www.gecode.org/mailman/listinfo/gecode-users

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