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

[Kish Shen]

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


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