[gecode-users] Optimization

[Peter Vanhee]

Hi all,

I am working on an optimization problem defined using constraints,
to compute the lowest energy model of a protein lattice. My variables are
implemented as integer variables that refer to a pool of protein fragments,
and I wish to implement an optimization function that - given an assignment
of all variables - returns an energy value (double) that should be minimized.

So far, I've implemented the optimization as follows:

- in the model constructor, I use synchronized execution to call a function
c when all variables become assigned (using wait(Space&, IntVarArray&, c&)

- a static variable that holds the best energy so far

static BEST_ENERGY = 10000;

- the continuation function c looks something like 

static void c(Space& _home) {
	// compute energy using assigned variables
	double energy = ...;

	if(energy > BEST_ENERGY) {
 		// fail if energy is worse
		home.fail();
	} else {
		BEST_ENERGY = energy;
	}
}


This works fine, and I can use different search algorithms to traverse the tree
and move into the direction of lowest energy. However, I am not sure if this is the 
correct way. Initially, I thought about implementing the cost() function but quickly
discarded it because it only seems to work with integer variables. Also using the
constrain function I need to use a static variable as well, and I don't know what
kind of constrained I should post there (the energy function can not prune domains,
it can either accept it as better or fail the space..)

Thanks for the clarification!
Peter