SAT solver set default result(cryptominisat)

Question

I'm modeling a problem with SAT and trying to solve it with cryptominisat. I'd like to give my variable a default value if there's no constraint for it.

I went through the manual and set_default_polarity seems like the answer. I tried it out but it doesn't work as I expected. I don't really get the term polarity here. Some googling didn't help me out as I'm not familiar with logic.

So, my questions are:

Would you kindly explain what polarity is or point me to some introductory-level sources?
Is there an interface in cryptominisat(or in SAT solvers generally) to set default value for logic variables? What is the term for such functionality?

Thanks.

Axel Kemper · Answer 1 · 2017-08-01T19:45:46.553

cryptominisat --hhelp (note the extra h!) gives the following extended help:

.....
  --polar arg (=auto)                   {true,false,rnd,auto} Selects polarity
                                        mode. 'true' -> selects only positive
                                        polarity when branching. 'false' ->
                                        selects only negative polarity when
                                        brancing. 'auto' -> selects last
                                        polarity used (also called 'caching')
.....

I use --polar=false to let cryptominisat search for solutions with false/0 variables first, because my examples have most solution variables that way.

In the source, this corresponds to solverconf.h:

enum class PolarityMode {
    polarmode_pos
    , polarmode_neg
    , polarmode_rnd
    , polarmode_automatic
};

The respective SolverConf variable is PolarityMode polarity_mode

In main.cpp is shown how to set this configuration property in a program:

if (vm.count("polar")) {
        string mode = vm["polar"].as<string>();

        if (mode == "true") conf.polarity_mode = polarmode_pos;
        else if (mode == "false") conf.polarity_mode = polarmode_neg;
        else if (mode == "rnd") conf.polarity_mode = polarmode_rnd;
        else if (mode == "auto") conf.polarity_mode = polarmode_automatic;
        else throw WrongParam(mode, "unknown polarity-mode");
    }

Other SAT solvers are using terms like phase or sign.

Microsoft Z3 can be parameterized via commandline sat.phase=always_false to try false phase first. See a related question. Actually, my first question on StackOverflow back in 2012.

Clasp is using commandline syntax --sign-def=neg to take false polarity first.

SAT solver set default result(cryptominisat)

1 Answers1