[gecode-users] Extending Integer Variable

[Christian Schulte]

A good overview is provided by the chapter "Continous and Interval
Constraints" by Benhamou and Granvilliers in the Handbook of Constraint
Programming. Maybe you can find the chapter online.

Cheers
Christian


On 4/8/08 10:13 AM, "Filip Konvička" <filip.konvicka at logis.cz> wrote:

> 
>> Well, nothing is easy ;-)
>> 
>> As it comes to double one should keep in mind that most CPUs have parallel
>> functional units for floats: so, that just runs in parallel to the integer
>> and address arithmetic. I once did a little profiling to see what effect it
>> has for double and it was considerably less than what I had expected. The
>> big problem with doubles start if you store them in memory, bandwidth and
>> alignment are the typical problems. But for intermediate results that should
>> be okay. But I agree, 64 bit should also be fine. The reason why we didn't
>> go for that is that I looked at the assembly code that was generated by gcc
>> at that time (maybe three years ago)... It just made me cry. As soon as long
>> long becomes C++ standard (maybe relying on the de-facto C++0x standard -
>> most likely C++09 - would already be good enough) we will go for 64 bits.
>> The main motivation for us is that we use double only for integers which
>> limits precision to 48 bits.
> 
> :-) I think I've seen some discussions on the gcc mailing lists
> concerning long long arithmetics, maybe some year ago or so...so maybe
> it is better now.
> 
>> 128 bits can be tinkered okay. Either rely on compiler extensions and if
>> they are not available hack it yourself.
>> 
>> Yes, however small the set of propagators might be, we will be interested. I
>> would believe that much of the IntVar stuff can serve as a good starting
>> point for you. If one gets really serious about float intervals, it becomes
>> tricky: it requires symbolic representation of the arithmetic expressions as
>> well as variable centered propagation. Quite different.
> 
> That's interesting. (Read: I don't understand that :-)) What is
> variable-centered propagation? Do you have any papers about the matter?
> The only implementation of floatvars I've seen so far is the XRI library
> for Mozart, so I was not thinking about doing anything special yet.
> 
> I can see that symbolic representation can be useful, but it depends on
> what quality/performance ratio you target. Personally I target
> performance (the tradeoff I see here is that I might not get bit-precise
> filtering).
> 
>> Watch out: for some x64 it is still that long is 32 bits (Windows). On
>> others it is 64 (MacOS, Linux?). Only long long is 64 at least.
> 
> Yes, I was referring to gcc. On Windows things tend to be
> backwards-compatible as *long* as possible :-D
> 
> Cheers,
> Filip
> 
> 
> _______________________________________________
> Gecode users mailing list
> users at gecode.org
> https://www.gecode.org/mailman/listinfo/gecode-users

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