Allow configuring of migration direction in UnidirectionalRingMigrator

[pfleck]

Currently, the UnidirectionalRingMigrator migrates individuals by shifting the Selected-Scope of each subpopulation to the left.

Although, the direction of the migrator makes no difference for the IslandGA, for algorithms like ALPS the direction is important.

Therefore the direction of the migration should be configurable for the UnidirectionalRingMigrator (left or right).

[pfleck]

mkommenda also suggested the UnidirectionalRingMigrator should migrate clockwise per default, therefore moving the scopes to the right per default.

This does not break any compatibility problems, however old runs are not repeatable with the same seed since the migration direction would be changed.

[pfleck]

#2495

• Added ClockwiseMigrationDirection Parameter.
• Added backwards compatability hook that use the old counterclockwise migration.

Sample Selected Scopes for Migration A B C D E

Old migration: B C D E A (shifted left)

New migration: E A B C D (shifted right)

[pfleck]

r13094 Added backwards compatibility for IslandGeneticAlgorithm and IslandOffspringSelectionGeneticAlgorithm to still use counterclockwise migration. The UnidirectionalRingMigrator uses clockwise per default.

[mkommend]

Review comments

UnidirectionalRingMigrator

• I would suggest to name the parameter ClockwiseMigration (shorter and simpler)
• Remove property to access the BoolValue directly
• Update documentation of ApplyMethod

Other than that the code looks fine.

[pfleck]

r13109

• Renamed ClockwiseMigrationDirection ClockwiseMigration.
• Removed access property.
• Updated documentation comments.

[ascheibe]

Thanks, looks good!

[ascheibe]

r13134: merged r13078, r13094 and r13109 into stable