Question: Polarity Heuristic of clasp

[mahi045]

It is a question: As I checked the code, clasp maintains the following hierarchy to choose the polarity of a variable:

user > saved > preferred > current sign score of heuristic > default value

I am interested to know about the purposes of different types of values (e.g., user and preferred values). Thanks in advance.

[rkaminsk]

This question might be better asked at the clasp project (@BenKaufmann). I think (but don't know) the values are related to the different heuristics offered by clasp:

• user: The domain heuristic allows for selecting the sign based on rules.
• saved: There is the progress saving heuristics (also phase saving heuristics) that restores signs after restarts.
• preferred: I don't know.
• current: Related to the sign selection heuristic configurable via the command line.
• default: Default signs can be configured via the command line.

[BenKaufmann]

@rkaminsk @mahi045 As an addition: the "preferred" type is currently only used if option "--opt-heuristic" contains "sign". In that case, variables occurring in a minimize statement have their "preferred" polarity set to the value that minimizes their overall weight.

[mahi045]

Thanks to @rkaminsk and @BenKaufmann. Please clarify the following points:

• user: makes sense only for domain heuristic
• preferred: makes sense only for optimization problems.
• current: makes sense if there is no saved value for a variable
• default: makes sense if I specify the polarity via the command line

[rkaminsk]

I am not sure what you are trying to ask here. Do you know about he different command-line options we are referring to?

Thanks to @rkaminsk and @BenKaufmann. Please clarify the following points:

* user: makes sense only for domain heuristic

* preferred: makes sense only for optimization problems.

* current: makes sense if there is no saved value for a variable

* default: makes sense if I specify the polarity via the command line

[mahi045]

Sorry for the confusion. I have checked the command-line options you mentioned earlier. I tried to say:

• clingo uses user values in domain heuristic only.
• clingo uses preferred values if "--opt-heuristic" option contains signs.
• clingo uses current values of a variables if there is no assignment to this variable in the (polarity) cache.
• clingo uses default values if we specify "--sign-def" option in the command line.

Does it look good now?

[BenKaufmann]

Some minor additions:

• The user value is influenced by the domain heuristic, either via Heuristic statements (of type sign) in the (aspif) input or via the "--dom-mod" command-line option.
• The saved value is typically only used if option "--save-progress" is active
• If available, the current sign score of the active heuristic is used for a variable if it has no user, saved, or preferred value
• The default value is typically only used when computing brave/cautious consequences.
• The value specified via "--sign-def" is only used if none of the previous values applies

[mahi045]

Thanks, @rkaminsk, and @BenKaufmann, for the detailed information.