[gecode-users] Strange branching behaviour when using FunctionBrancher

[Christian Schulte]

Forget about status(), that will not help you here... Sorry!

 

Cheers

Christian

 

--

Christian Schulte, Professor of Computer Science, KTH, www.gecode.org/~schulte/

 

From: Andrea Peano [mailto:andrea.peano at unife.it] 
Sent: Tuesday, September 23, 2014 2:25 PM
To: Christian Schulte
Cc: users at gecode.org
Subject: Re: [gecode-users] Strange branching behaviour when using FunctionBrancher

 

On Tue, Sep 23, 2014 at 2:09 PM, Christian Schulte <cschulte at kth.se> wrote:

You can disable recomputation but this is not a good idea as it degrades performance seriously and increases memory consumption considerably.

Yes, I see.

 

 

What you could do (also not good) is call status() yourself.

I'm already doing it, but this does not seem enough to prevent recomputation on those nodes. I call it within second_level and third_level but it's not enough. Do you mean somewhere else?

 

 

The real (but tough) thing to do is to implement your own brancher. 

 

And just checking: do you know that multiple branchers are executed in the order they are created? But maybe that is not enough for you.

Yes, I know, I tried to make the search as simple as possible, but there are some aspects of the problem a bit difficult to manage.

Anyway, I'll find a way.

 

Thanks for giving me a halping hand.

 

Andrea

 

 

Cheers

Christian

 

--

Christian Schulte, Professor of Computer Science, KTH, www.gecode.org/~schulte/

 

From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf Of Andrea Peano
Sent: Tuesday, September 23, 2014 2:00 PM
To: users at gecode.org
Subject: Re: [gecode-users] Strange branching behaviour when using FunctionBrancher

 

I was just reading on the Gecode guide that this behaviour is due to the "recomputation".

So I have two more questions: can I completely prevent this behaviour by disabling recomputation?

Has recomputation a direct effect on parallel search?

 

Thanks,

Andrea

 

On Tue, Sep 23, 2014 at 1:22 PM, Andrea Peano <andrea.peano at unife.it> wrote:

Hello,

 

I've implemented a search strategy by splitting the search into three levels. I think the code may explain better this strategy.

 

 

void MyModel::post(Space& home)

{

static_cast<MyModel&>(home).second_level();

}

 

void MyModel::second_level()

{

status();

 

//do something with the partial solution
//print "second level"

branch(*this, BoolBranchDirection, INT_VAL_MIN());

branch(*this, post2);

}

 

void MyModel::post2(Space& home)

{

static_cast<MyModel&>(home).third_level();

}

 

void MyModel::third_level()

{

if(BoolBranchDirection.val()==0)
{
//print third level left
//left branch behaviour (install further branches)
}
else
{
//print third level right
//right branch behaviour (install further branches)
}

}

 

Imagine now we are fixing the partial solution before the "post" calling, so the solver goes only once into the "post" function (and it's confirmed by GIST).

 

The strange fact is that "second_level" is called more than once! Instead I expect one call for "second_level" and two calls for "third_level", which executes two different paths of the code.

 

These are the prints I read:

second level

third level left

second level

third level right

second level

third level right

 

But I expected:

second level

third level left

third level right

 

Can you clarify this behaviour please?

 

Furthermore, I experienced that I need to call "status()" within the second level, to ground some variables I expected to be already ground. Is this normal?

 

I'm using Gecode 4.2.1

 

Thanks,

Andrea

 

 

-- 

 

Andrea Peano - PhD student

Department of Engineering - University of Ferrara

Tel: +39 0532 97 4827





 

-- 

 

Andrea Peano - PhD student

Department of Engineering - University of Ferrara

Tel: +39 0532 97 4827





 

-- 

 

Andrea Peano - PhD student

Department of Engineering - University of Ferrara

Tel: +39 0532 97 4827

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