Information Technology Reference
In-Depth Information
excessive population growth, proliferation candidates only undergo proliferation
if their SF or ML values exceed those attained in the previous generation. The
tracker is seen to have improved its fitness to an antigen trend (in terms of length
of match, or frequency of occurrence) and as such is cloned.
4.3
Proliferation and Mutation
All trackers that meet the proliferation criteria are cloned, forming the short term
memory pool theorised in Section 3. The number of clones generated during a
match is proportional to the ML for that match. This was decided because a
proliferation mechanism, using ML as a driver, in conjunction with the mutation
mechanism, encourages successful trackers to evolve and lengthen to match ever
longer trends.
Clones undergo mutation within the TEA in one of two unique forms, selected
randomly with a probability of 0.5.
-MutationbyExtension:
Here a new price estimate is generated randomly
using a Gaussian distribution and added to the end of the clone.
- Mutation by Shortening:
Here a randomly selected price estimate within
the tracker is eliminated.
Extension mutation allows the clone, whose parent was a successful match
to a trend, to anticipate the next price movement in that trend. The tracker
clone evolves to increase the length of it's MS as it tries to detect longer and
more complex price trends. During the binding process some trackers will contain
redundant price information. Redundant price information is defined as any price
values within the tracker that are not included in the MS of that tracker. The
shortening mutation permits the trackers a random chance to rid themselves of
redundant information and improve the accuracy of the resulting memory pool.
4.4
Long Term Memory Transfer
During each generation all trackers undergoing proliferation become candidates
for entry into the long term memory pool. Trackers that have a MS not recorded
in the memory pool will automatically be transferred into the pool for preser-
vation. Candidates with a MS identical to that of one of the memory trackers
will only replace that memory if they contain less redundant information than
that memory tracker. The memory pool thus reflects the most ecient matching
trackers in the population up to that point in time.
4.5
Apoptosis
To ensure the tracker population returns to a stable equilibrium 10% of the
current tracker population is selected at random and eliminated. Both high and
low anity trackers have the same probability of death. If the population falls
below its minimal limit of 20 the remaining population will automatically clone
to repopulate the pool, reflecting homeostatic turnover observed in nature.
