Change propagator argument parameters between Branch and Bound solutions

[John]

Hello. I would like to use Branch and Bound with a custom propagator, and each time a solution is found, to access the solution and use it to change some argument parameters of the propagator, for the search of the next solution. The motivation is that as BAB restricts the cost of the solutions more and more, the propagator can also adapt using the latest solution and perform more optimized internal reasoning. What is the best way to achieve this in Gecode? 

Thank you.

[Mikael Zayenz Lagerkvist]

Hi John,

While Gecode has support for standard cost-variable optimization via
e.g. IntMinimizeSpace, the base construction is more general. When
search recommences after a solution has been found in BAB search, the
constrain method is called for the current Space with the last
solution found (https://www.gecode.org/doc-latest/reference/group__TaskModelScript.html#ga90b963e8bbaa9c832f97a5bc9598b455).
This can be used for "just" updating the bounds on an integer
variable, but also for other types of information. See also chapter
2.5 in MPG.

For storing and accessing the data, a shared object that is also
stored in the Space is probably a good idea, depending on the type of
information needed. See chapter 31.3 in MPG.

Cheers,
Mikael

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Mikael Zayenz Lagerkvist