[gecode-users] mzn-gecode search strategy

[Guido Tack]

Hi Tias,

it's slightly complicated (and it has changed in Gecode 4).  The default search is implemented in gecode/flatzinc/flatzinc.cpp in function createBranchers, and the defaults in 4.0.0 are

    branch(*this, iv_sol, INT_VAR_AFC_SIZE_MAX(0.99), INT_VAL_MIN());
    branch(*this, bv_sol, INT_VAR_AFC_MAX(0.99), INT_VAL_MIN());
    branch(*this, fv_sol, FLOAT_VAR_SIZE_MIN(), FLOAT_VAL_SPLIT_MIN());
    branch(*this, sv_sol, SET_VAR_AFC_SIZE_MAX(0.99), SET_VAL_MIN_INC());

where iv_sol are the variables mentioned in the output statement and not mentioned in an explicit search annotation, and

      branch(fzs,fzs.iv_aux,INT_VAR_AFC_SIZE_MAX(),INT_VAL_MIN());
      branch(fzs,fzs.bv_aux,INT_VAR_AFC_MAX(),INT_VAL_MIN());
      branch(fzs,fzs.sv_aux,SET_VAR_AFC_SIZE_MAX(),SET_VAL_MIN_INC());
      branch(fzs,fzs.fv_aux,FLOAT_VAR_AFC_SIZE_MAX(),FLOAT_VAL_SPLIT_MIN());

where iv_aux are variables introduced by mzn2fzn that are not functionally defined.

I'm planning to introduce annotations default_{int,bool,set,float}_search that you can stick on the solve item to change the default for the different variable types - would that be useful?

Cheers,
Guido

On 16/04/2013, at 2:22 AM, Tias Guns <tias.guns at cs.kuleuven.be> wrote:

> Hi Guido,
> 
> What is the default search strategy of gecode's fz interpreter?
> 
> Its default search works really well on one group of variables, but less on the other. I want to change it for the other, but whatever I do the search is a lot slower (because of worse choices on the variables I do not wish to change the order on)...
> 
> I couldn't find it on http://www.gecode.org/flatzinc.html or MPG.
> 
> 
> Thanks,
> Tias
> 
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