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

[Christian Schulte]

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> 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

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--
Dr. Pascal Francq
Belgium

 



-- 
Dr. Pascal Francq
Belgium

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