[SMTCOMP] About the QF_IDL "n-queens" problms

[Leonardo de Moura]

Dear Roberto,

We are aware of the problem. The n-queens benchmarks were marked
as crafted. The benchmark selection algorithm uses the following
distribution: 85% industrial, 10% crafted, 5% random.
In our simulations, only 4 queens problems were selected.
You can find more information about the benchmark selection
algorithm at:
http://www.csl.sri.com/users/demoura/smt-comp/bench_selection.shtml

Cheers,
Leonardo


On Jul 7, 2006, at 10:00 AM, Roberto Sebastiani wrote:

> Dear colleagues,
>
> Let me raise one more point, about "n-queens" problems in the  
> QF_IDL benchmark suite. (I apologize for doing it only now, but we  
> noticed this fact
> only recently.)
>
> 297 out of 893 total benchmarks in QF_IDL  are "n-queens".
> It seems to us they are all "pigeonhole-style" problems:
>
> 1. { x_i != x_j }_{ij}
> 2. { x_i=value_{i_1} | x_i=value_{i_2} | ... | x_i=value_{i_K} }_i
>
> which are encoded into QF_IDL as
>
> 1.1. { x_i != x_j }_{ij}
> 2.1. { {i_1}  <= x_i-zero <= i_K }_i
>
> ("zero" being one variable representing zero).
>
> Thus, they are FULLY-COMBINATORIAL CSP PROBLEMS disguised as SMT 
> (QF_IDL) problems, and have hardly anything to do with QF_IDL.
> In fact, no  arithmetical property should be exploited to solve  
> these problems.
> (Notice, e.g., that the actual values of the constants value_ 
> {i_j}'s are irrelevant: the only relevant fact is weather they are  
> pairwise equal or different. Thus. "-" and ">=" have no effective  
> mathematical meaning here.)
>
> We believe this is against the spirit of SMT-COMP.
> Moreover, these are the kind of problems which may push people to  
> customize "ad hoc" solutions for the competition.
>
> Thus, we believe these problems should be dropped from the list.
>
> Roberto
>
>
> -- 
> ------------------------------------------------------------------
> Prof. ROBERTO SEBASTIANI
> Dip. Informatica e Telecomunicazioni
> Fac. Scienze M.F.N., Universita` di Trento    Tel: +39 0461 881514
> Via Sommarive 14, I-38050, Trento, Italy      Fax: +39 0461 882093
> roberto.sebastiani at dit.unitn.it     http://www.dit.unitn.it/~rseba
> ------------------------------------------------------------------