[gecode-users] Computing Variable Domains
Max Ostrowski
ostrowsk at cs.uni-potsdam.de
Tue Aug 14 09:33:44 CEST 2012
OK, i see.
This was indeed the thing i wanted to do.
I had some bad experiences with posting propagators on unrestricted
variables.
Given that my supports has a declarative language for the description of
the constraints, no domain is given as input.
That why i wanted to compute one.
But i will now leave it with a simple bound computation using
boost::numeric::interval.
Thanks a lot,
Max
On 08/14/2012 06:52 AM, Guido Tack wrote:
> Sorry but I'm not sure I understand what you're trying to do. Are you
> trying to precompute bounds on the domains of a and b given that there
> is a constraint a+b=c in your model? We don't have specialised
> iterators for that kind of computation, and just running propagation
> (i.e. calling status once) will give you the same result. You should
> only restrict the variables to reasonable initial domains (i.e., use
> some easy to compute upper and lower bounds). But you don't have to do
> the propagators' job.
>
> Cheers,
> Guido
>
> On 13/08/2012, at 8:57 PM, Max Ostrowski <ostrowsk at cs.uni-potsdam.de
> <mailto:ostrowsk at cs.uni-potsdam.de>> wrote:
>
>> Thank you very much for the fast answer.
>> I tried to play around with them but still face a lot of problems.
>>
>> In the documentation
>> http://www.gecode.org/doc-latest/reference/group__FuncIterRangesVirt.html
>> it is written that
>> "Iterators with virtual member functions have to be used when they
>> are combined dynamically ..."
>> The only base class i found is MinMax.
>>
>> So how can i use the iterator dynamically.
>> In the given example i have to know the type of the iterator used before.
>> (To build the intersection of two Singletons for example)
>> But if i want to build the intersection of two "domains" which could
>> have been constructed in various ways (for example recursively),
>> i need to have a general Base Type, right ?
>> Is the Iter::Ranges thing still the right thing to use or is there
>> something else.
>>
>> Also i found only iterators for union/intersection etc...
>> Given that you want to add two variables a and b with known domain
>> (stored in a RangeList?), how do you compute the domain of the result.
>> Is there any functionality for this or do i have to iterate through
>> both lists of ranges and add them together to form a new list.
>>
>>
>> I hope i made things clear, if not please ask.
>>
>>
>> Best,
>> Max
>>
>>
>> On 08/10/2012 06:44 AM, Guido Tack wrote:
>>> Hi,
>>>
>>> here's some code that will do what you want:
>>>
>>> Iter::Ranges::Singleton si00(6,Int::Limits::max);
>>> Iter::Ranges::Singleton si10(Int::Limits::min,9);
>>>
>>> Iter::Ranges::Inter<Iter::Ranges::Singleton,Iter::Ranges::Singleton>
>>> inter0(si00,si10);
>>>
>>> Iter::Ranges::Singleton si01(101,Int::Limits::max);
>>> Iter::Ranges::Singleton si11(Int::Limits::min,104);
>>>
>>> Iter::Ranges::Inter<Iter::Ranges::Singleton,Iter::Ranges::Singleton>
>>> inter1(si01,si11);
>>>
>>> Iter::Ranges::Union<
>>>
>>> Iter::Ranges::Inter<Iter::Ranges::Singleton,Iter::Ranges::Singleton>,
>>>
>>> Iter::Ranges::Inter<Iter::Ranges::Singleton,Iter::Ranges::Singleton> >
>>> u(inter0,inter1);
>>>
>>> IntVar a(*this,IntSet(u));
>>>
>>> You can also use the n-ary variants of the iterators if you need to
>>> compute a union or intersection of more than two sets.
>>>
>>> Cheers,
>>> Guido
>>>
>>> On 08/08/2012, at 9:41 PM, Max Ostrowski <ostrowsk at cs.uni-potsdam.de
>>> <mailto:ostrowsk at cs.uni-potsdam.de>> wrote:
>>>
>>>> Sorry for reposting an old question. I'm just cleaning up my code
>>>> and noticed that i still not managed to use gecode's functionality
>>>> to precompute domains of IntVar.
>>>> So, given a constraint "(a>5 /\ a<10) \/ (a>100 /\ a<105)"
>>>> I want to precompute the domain of "a".
>>>> I'm simply not able to find out how the Ranges iterators are used.
>>>> How to i create a range "5..inf" and a range "-inf..10"
>>>> How do i create the intersection of both.
>>>> And finally how to set the domain of IntVar x to this range then.
>>>>
>>>>
>>>> I tried to grep the gecode code and the examples but was not able
>>>> to find any.
>>>>
>>>> Sorry again for reposting this, i'm ashamed.
>>>>
>>>> Best,
>>>> Max
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> The best is to look for examples in the code ;-) Just grep for it.
>>>>
>>>> MinMax is nothing but a base-class for other classes and cannot
>>>> be used
>>>> directly. Look for the iterators that take arrays as input,
>>>> they will do what
>>>> you want.
>>>>
>>>> Best
>>>> Christian
>>>>
>>>> --
>>>> Christian Schulte, KTH, web.it.kth.se/~cschulte/
>>>> <http://web.it.kth.se/%7Ecschulte/>
>>>>
>>>> -----Original Message-----
>>>> From: users-boun... at gecode.org
>>>> [mailto:users-boun... at gecode.org] On Behalf Of
>>>> Max Ostrowski
>>>> Sent: Thursday, July 21, 2011 10:49 AM
>>>> To: users at gecode.org
>>>> Subject: [gecode-users] Computing Variable Domains (Integer)
>>>>
>>>> Hello everybody,
>>>>
>>>> as variables in gecode need to have a domain, i want to compute
>>>> the domain of
>>>> the variables automatically, given the constraints.
>>>> I could also let the constraints restrict the domains of my
>>>> variables, but as i
>>>> understood, this is similar to propagation and could take some
>>>> time.
>>>> There i want to restrict the domain manually for all unary
>>>> constraints.
>>>> So, given a constraint "(a>5 /\ a<10) \/ (a>100 /\ a<105)"
>>>> the domain should be {6..9,101..104}.
>>>> Therefore i wanted to use some Gecode classes to compute the
>>>> intersection/union/complement etc.. of the sets.
>>>> Am i right that i can use the Int::Iter::Ranges classes for this?
>>>> And second, how do they work?
>>>> So in this case, i would create a
>>>>
>>>> IntSet a1(Gecode::Iter::Ranges::MinMax(5+1,Int::Limits::max));
>>>> IntSet a2(Gecode::Iter::Ranges::MinMax(Int::Limits::min, 10-1));
>>>>
>>>> And them somehow the intersection of this.
>>>> But i was neither able to initialize a set with a Range, nor to
>>>> combine Ranges
>>>> recursively.
>>>>
>>>> So, how do i do this using the helping classes of gecode.
>>>>
>>>> Best,
>>>> Max
>>>>
>>>> _______________________________________________
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>>>
>>
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