[gecode-users] doing multiple minimising searches with the same space

[Kish Shen]

Christian Schulte wrote:
> Hi Kish,
> 
> That's indeed C++-ish: the meaning of the assignment is defined by the
> assignment operator of the left hand side... For an IntView it's quite
> simple: it just redirects the left hand side IntView to point to the
> variable implementation of the right hand side. Whatever was on the left
> hand side will be gone. Almost like in Eclipse provided the left hand side
> was a yet unbound and unconstrained var. You might want to check Section 4.1
> in MwG.
> 
> Is that an answer to your question?
> 
> Cheers
> Christian
> 
> --
> Christian Schulte, www.ict.kth.se/~cschulte/
> 
> 
> -----Original Message-----
> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
> Of Kish Shen
> Sent: Tuesday, July 21, 2009 7:08 PM
> To: Guido Tack
> Cc: Christian Schulte; users at gecode.org
> Subject: Re: [gecode-users] doing multiple minimising searches with the same
> space
> 
> Guido Tack wrote:
>> Christian Schulte wrote:
>>> There is special support for specialized "constrain" functions which just
>>> return a cost variable, you might want to check that in "Modeling with
>>> Gecode". Rather than fixing a particular cost variable you can use a cost
>>> function that then decides which variable to return depending on which 
>>> cost
>>> variable you want use now. Remember: any problem can be solved with one
>>> additional level of indirection ;-)
>> Exactly!  You can even use actual assignment instead of an equality 
>> constraint.  I.e., your space has a member "IntVar cost" that the cost 
>> function returns.  When you initialize optimization for variable x, you 
>> execute "space.cost = x" instead of posting the constraint "rel(space, 
>> cost, IRT_EQ, x)".  That way, you can change that assignment later when 
>> you start the next search!  You just have to make sure that you actually 
>> do make such an assignment before you start search, and that you update 
>> cost (as usual) in the copy constructor.
>>
>> Cheers,
>>     Guido
>>
> Hi Christian and Guido,
> 
> Thanks for your replies!
> 
> I was looking at the "Modelling with Gecode", or at least an early 
> version that Guido sent me. What I wasn't aware of was that you can do a 
> simple assignment between two IntVars, as in "space.cost = x". This 
> probably reflect my lack of knowledge in C++, but what exactly does such 
> an assignment mean?
> 
> Thanks and cheers,
> 
> Kish
> 

Hi Christian,

Thanks for the quick reply. I think that does answer my question. It is 
like the assignment of a pointer in C.

Cheers,

Kish
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