[gecode-users] How to estimate the range of a (linear) function

[Christian Schulte]

The simplest option is to use the minimodel support for writing linear
expressions, so in your case: instead of creating a variable y yourself,
just set y to the variable that is returned by the expr function, that is,
something like:
	IntVar y = expr(home, c+5*7-b);
The expr function actually does infer tight bounds for the variables it
returns (based on the domains of c and b in this example). If that does not
fit your bill you might want to check how expr does it. Not that difficult,
in fact.

The problem is that one should always keep in mind that the basic
abstraction in CP are relations (constraints). Anything that involves
expressions requires additional effort. That is one reason why the basic
layer in Gecode talks about constraints only and has an additional layer of
abstraction (minimodel) to deal with expressions.

Christian

--
Christian Schulte, KTH, web.it.kth.se/~cschulte/


-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Max Ostrowski
Sent: Friday, June 10, 2011 10:42 AM
To: users at gecode.org
Subject: [gecode-users] How to estimate the range of a (linear) function

Hello everybody,

as i'm developing an SMT-like solver, i have a special syntax for the
constraints of Gecode and i also have to handle things.

b(1..3).
$count[a(X) $== c+5*7-b : b(X)] $> 0.


This shall represent an count constraint constraint.
count(x,y,>,0) where x is a set of variables (a(1),a(2),a(3)) and y is a
single variable y=c+5*7-b.
The domains of the variables a,b,c are known (usually an IntSet).
I created a variable for "c+5*7-b" using the domain
(Limits::min,Limits::max).
I found out that this is not the best way to do it, as Gecode does not seem
to automatically shrink the domain of y :-)


Is there some functionality in Gecode for automatically/manually estimate
the range of a function. (So if i add a and b, can't i just "add" the domain
of them using the IntVarRanges?).
And the same for multiplication etc...

Thanks in advance,

Max
--
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bis zu 50,- Euro! https://freundschaftswerbung.gmx.de

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