Global:
The global solver used by the NIMBUS system is based on a genetic algorithm.
There is two different versions of the global solver, named as Global
1 and Global 2. The underlaying genetic algorithm in is identical in
both global solvers, they differ only by their constraint handling routines.
Global 1:
The global solver is genetic algorithm together with the constraint handling
technique suggested by Deb. Infeasible solutions are avoided in
the selection phase so that feasible solutions are always preferred
to infeasible ones. If the selection is to be done between two
infeasible solutions, the one closer to the feasible region is selected.
This constraint handling technique involves no additional parameters.
Global 2:
The global solver is genetic algorithm together with the method of adaptive
penalties (AP) for handling constraints. The AP method tries to avoid
infeasible solutions by adjusting the penalty coefficient. The penalty is
increased if all the best solutions of a pre-specified number of
past iterations are infeasible whereas the penalty is decreased if all of them
are feasible.
Hybrid:
In a hybrid method the global and local methods have been combined. In
a hybrid method the problem is first solved with and global solver,
and then the obtained solution is solved the local method.
Global 1 + Local (PB):
In Global 1 + Local (PB) method the Global 1 has been
combined with the Local (PB) method. These methods are described earlier.
Global 2 + Local (PB):
In Global 2 + Local (PB) method the Global 2 has been
combined with the Local (PB) method. These methods are described earlier.
nimbus@mit.jyu.fi