[gecode-users] On posting bin packing constraints

[Christian Schulte]

Hi Stefano,

Completely agree and has already been requested by other users, so it is
already in the trunk!

But thanks for pointing out!

Cheers
Christian

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


> -----Original Message-----
> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On
> Behalf Of Stefano Gualandi
> Sent: Thursday, March 07, 2013 2:35 PM
> To: users at gecode.org
> Subject: [gecode-users] On posting bin packing constraints
> 
> Hi,
> as a user, I have a very a simple suggestions about posting a bin packing
> constraint when one of the item has size equals to zero.
> 
> The documentation is quite clear (if it took a while to find this out),
Gecode
> raises an exception whenever:
> 
> >> Of type Int::OutOfLimits if s contains a non-positive number.
> 
> Items with negative sizes are not supported by the filtering algorithm,
fine.
> 
> However, for an item with size equals to zero, this is a bit too severe.
> An item of size equals to zero never makes the constraints invalid.
> When you have several bin packing constraints over the same set of items
(due
> to several dimensions of each item) it might be that one of the dimensions
is
> zero for one or more items.
> 
> Therefore, I would suggest to simple ignore the IntVar associated to an
item of
> zero size, as follows (ugly code, but it is to give you the idea). Since
you pass the
> variable views to the propagator, indeed you may ignore the view of zero
size
> variables.
> 
> cheers,
> Stefano
> 
> 
> 
> file: bin-packing.cpp (geocode 3.7.3):
> 
>     [.]
>     int items=s.size();
>     for (int i=s.size(); i--; )
>        if (s[i] == 0)
>           items--;
>        else
>           Limits::positive(s[i],"Int::binpacking");
> 
>     [.]
> 
>     ViewArray<BinPacking::Item> bs(home,items);
>     for (int i=s.size(), j=0; i--; )
>        if ( s[i] > 0 )
>           bs[j++] = BinPacking::Item(b[i],s[i]);
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