[gecode-users] performance issues

[Kish Shen]

Hi Christian,

An update to my performance problem: the problem was after all caused by 
my new code, rather than Gecode. The reason is that the search in that 
example uses the #= and #\= constraints to set/exclude values from a 
variable's domain, and the conversion of these constraints into Gecode 
calls is precisely the code I changed, and this code is now more 
expensive, as it has to deal with various types of expressions.

The overhead with these constraints are probably unavoidable, and in 
most cases the overheads are not significant when they are only used 
during modelling, rather than in the search as in this case.

I changed the example to directly assign the value instead of using #=, 
and used refified domain constraint (with the boolean set to 0) to 
exclude a value, and the execution is now faster, probably even faster 
than the old results.

I have also been thinking about your last reply:

Christian Schulte wrote:

> If you post constraints on the IntVars before their domain is reduced to
> 0..1 then some propagators might have to resort to a less efficient
> representation. The difference can range from anything like 10% (linear
> constraints, for example) to 50% (extensional constraints, for example). 

This should not happen -- what happens is that my code now extract all 
new variables from an expression, and add them to gecode with a default 
domain, and then change any that are also booleans to the 0..1 domain.
This happens before any constraints are posted for these variables.

Cheers,

Kish

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