[gecode-users] exact behaviour of different IntValBranch

[Kish Shen]

Hi,

I am trying to understand how the different value selection strategies 
(IntValBranch) works. In particular, the exact behaviour after failures,
when a different value need to be selected.

I have always understood a value selection strategy (as used in ECLiPSe, 
for example), to define an order in which values from the domain of a 
variable is selected, i.e. the variable is set to the first value in 
this order, and on failures, the variable is set to the subsequent 
values in order.

 From reading Modelling with Gecode, I understand that most selections 
are done as binary choices, that is, a value is selected, and if another
value is required, the previously selected value is excluded from the 
domain (with propagation), before selecting the next value. I assume 
this does not apply to INT_VALUES_MIN/MAX. Are these the only exceptions?

For INT_VAL_MED, does this mean that the median is used for each 
selection? That is, you exclude the previous median value, and then
now select the new median in the updated domain? If this is the case,
does it mean the median has to be calculated each time? [this is a
relatively expensive operation in ECLiPSe's finite domain libraries,
and the for the "median" value selection strategy,  the median is 
calculated only once initially, subsequent selected values alternate 
between the next lower and higher value than the initial median].

For the INT_VAL_SPLIT* and INT_VAL_RANGE* strategies, the documentation
mention values (plural) being selected, rather than a single value. What 
does this mean exactly? I assume the variable still needs to be set to a
single value from the selected values? Does this simply mean that within 
the selected values, specific values are tried in some order, but 
without excluding previous values and propagating the consequences (as 
in INT_VALUES*, but not for the whole domain, just the selected values?).

Thanks in advance for any help and information!

Cheers,

Kish
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