[gecode-users] Update function

[Christian Schulte]

The model is that each space maintains its own variables, propagators, and
branchers. When you clone a space, also the variables must be cloned. That
is what update does. Just assigning the variable does not clone it by that
you would create two spaces sharing variables which does not work in Gecode.
This is not really an issue, just use update and that's it.

 

Best

Christian

 

--

Christian Schulte, Professor of Computer Science, KTH,
www.ict.kth.se/~cschulte/

 

From: zichenzu at gmail.com [mailto:zichenzu at gmail.com] On Behalf Of Zhu
Zichen's cse
Sent: Monday, November 11, 2013 9:07 AM
To: cschulte at kth.se
Cc: users at gecode.org
Subject: Re: [gecode-users] Update function

 

Dear Christian,

 

     Thanks for your reply. I read the chapter on Search, but I am still
confusing. For sequential search where shared always being true, when I
update a BoolVar x, why cannot I simply write x=OldSpace.x? It constraints
the two variables to take the same value. They might need extra propagation
compared with using update function, but the result should be same. Can you
help for this? Many thanks.

 

 

Zichen

 

On Thu, Nov 7, 2013 at 10:20 PM, Christian Schulte <cschulte at kth.se> wrote:

Hi,

 

The answer to the first question is simple: because you have to! Update
updates variables during cloning g and is needed for search. Posting a
constraint as you suggest is something very different.

 

There can be no global variables in Gecode provided you mean something such
as Gecode's integer variables as they are always situated inside a given
space (this is the space you given when initializing a Gecode variable). Or
dou you mean variable as in C++-variable? Then it does not need to be
updated.

 

Maybe you would like to read the chapter on Search in MPG that explains what
happens during search in Gecode.

 

Cheers

Christian

 

--

Christian Schulte, Professor of Computer Science, KTH,
www.ict.kth.se/~cschulte/

 

 

From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On Behalf
Of Zhu Zichen's cse
Sent: Thursday, November 07, 2013 3:12 PM
To: users at gecode.org
Subject: [gecode-users] Update function

 

Dear All,

          For variables, why do we have to use update function when we
copying? Why cannot I simply use rel(*this,x==_x)? And there are problems
when I use update function to update a global variable from another global
variable. What should I do when I update global variables?

 

 

Best Regards,

Zichen Zhu

 

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