[gecode-users] posting of expressions

[Christian Schulte]

Hi Kish,

There is one more thing that might be valuable to you: we have changed the
way how to post expressions and relations for the upcoming 3.4.0 (which
should be available end of this month at the latest). 

It is way more powerful (including arbitrary arithmetic expressions, set
variables, and so on) and distinguishes between a function expr() that posts
an expression (and hence returns a variable) and a function rel() that posts
a relation (and hence does not return a variable). This removes the
reification operator ~ and the confusion it caused.

Cheers
Christian 

--
Christian Schulte, web.ict.kth.se/~cschulte/


-----Original Message-----
From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Guido Tack
Sent: Tuesday, July 13, 2010 5:02 PM
To: Kish Shen
Cc: users at gecode.org
Subject: Re: [gecode-users] posting of expressions

Kish Shen wrote:
> As I have mentioned in my previous posts, I have been rewriting the code
for handling expressions for the ECLiPSe interface to Gecode. I am wondering
if there are any performance advantages in different ways of handling
certain special cases of expressions, like sum.
> 
> I had some special code that handled summation of variables using linear:
> 
> linear(*solver, vars, rel, sum)
> 
> where vars in IntVarArgs, sum is int (although I guess it could be
generalised to IntVar as well), and rel is IntRelType.
> 
> This code does not seem to be used at the moment, I assumed I had it to
handle some specific ECLiPSe code that I wanted to run quickly with the
interface.
> 
> Instead, such summed expressions are now handled through the general
expression handling code, and passed to Gecode as a LinRel through
minimodel. The sum is passed as a series of +, e.g. A+B+C rather than using
sum of a IntVarArg, because the code was written for Gecode 3.0.2, which I
don't think supported sum.
> 
> Is it more efficient to use the more specialised linear to post such
expressions, and is it more efficient to use sum in LinExpr rahter than a
series of +?

The minimodel layer will combine such expressions automatically, and post
the same propagators as when you call linear directly.  Of course, there's a
small overhead for the preprocessing of the LinExprs if you use a series of
+, but that should be hardly noticeable in practice.

Cheers,
	Guido

-- 
Guido Tack, http://people.cs.kuleuven.be/~guido.tack/





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