[gecode-users] sequence constraint: variable occurring multiply

[David Rijsman]

Hi Kish,

you are absolutely right, this extension is very useful for cyclical rosters. Should not be very hard to enable in the current implementation, basically changing the check at posting the constraint. I see if I can do this and see if this gets accepted?

David 

>>> 
From: 	Kish Shen <kisshen at cisco.com>
To:	<users at gecode.org>
Date: 	8/19/2010 2:03 AM
Subject: 	[gecode-users] sequence constraint: variable occurring multiply

Hi,

I have another question about the sequence constraint: exception 
ArumentSame is thrown if a variable occurs more than once. Should this 
exception be thrown? I can see that it does not make sense for a 
variable to occur in a subsequence of q variables, but if the 'distance' 
between the same variable > q, i.e. it cannot occur multiply in the same 
subsequence, should this be allowed? Can the implemented algorithm deal 
with this?

There are useful cases for variables to occur multiply, the simplest is 
a cycle, e.g. say for the following variables

x1,x2,x3,x4,x5

and a cycle would be

x1,x2,x3,x4,x5,x1,x2,....

such cycle could be used for a schedule that repeats.

Cheers,

Kish
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