Information Technology Reference
In-Depth Information
15.8.2
Avida
Avida is an adaptive genetic system, the concepts of which are similar to the
concepts of Tierra. Avida is obviously different from the traditional genetic
algorithm. The selection in Avida approaches the natural selection more closely
than most genetic algorithm mechanisms.
Avida system creates an artificial (virtual) environment inside the computer.
This system has implemented a virtual two-dimensional grid processor, which
runs a limited assembly language. The programs are stored in system memory as
consecutive strings of the commands. Each program (organism) is related to a
grid.
This program and its derivatives are influenced by various random mutations
subsequently. Any mutation, which results in the improvement of reproduction
capability in an appointed environment, is considered beneficial. Most mutations
are unfavorable (which typically make the organisms unable to reproduce
themselves completely) or neutral. Only a few beneficial mutations make the
organisms reproduce themselves more effectively and grow up stronger in the
environment. Through a period of time, the organisms which are more adaptive
to the environment appear. The important concepts of Avida system are as
follows:
1. Timesharing
Timesharing is the method of allocating the time to grid living beings, in which
they can occupy the processor and run their codes. Some living beings have the
processors faster than others, so the timesharing codes should confirm that they
run at the (relatively) appropriate speed. Each living being has an index which
determines its processor speed. Time allocator will adjust the indexes repeatedly
until the living beings are satisfied with task execution in the environment they
are located in. The timesharing mechanism has a far-reaching influence on the
overall behavior of the biological colony.
2. Adaptive degree
Adaptive degree is an unit-free measuring method, by which a particular
organism in some environment can measure its replication capability. Only in
comparison with others, can the adaptive degree of an organism make sense,
which provides the ratio of the replication rate of the organism to that of another
one. In order to compute the adaptive degree, divide the organism index by the
