Robotics Reference
In-Depth Information
authorship. An example of such a rule might be
If the word “but” appears more than 1.7 times per 1,000 words
then the text is by James Madison.
A single rule by itself might be very bad at discriminating between the
possible authors so Holmes and Forsyth created 100 rules and tested each
one of them on known texts written by Madison and Hamilton, arriv-
ing at a “fitness” score for each rule on the basis of how many of the
known texts it attributed correctly. The 50 “least fit” rules were then re-
moved from the set, small mutations were introduced into the surviving
50 rules in order to mimic evolution, and 50 new rules were added to
the set, restoring the total to 100. This process was repeated for 256
“generations”, at which point the evolved rules attributed all of the texts
correctly. When the evolved rules were then applied to the 12 disputed
Federalist papers they correctly attributed all 12 of them to Madison,
conforming exactly to the results of the analysis by Mosteller and Wallace
and to the established opinions of history scholars. What was remarkable
about the evolved rules created by the genetic algorithm is that they relied
on the statistics for only eight words.
Musical Style
Although stylometry has been applied to written texts for more than a
century, it is only very recently that any similar form of analysis has
been attempted in music. A method akin to that of literary stylome-
try has been employed by Dutch researchers Peter van Kranenburg and
Eric Backer. They trained their system using a set of 106 pieces of music
by Johann Sebastian Bach, 53 by Handel, as well as works by Telemann,
Haydn and Mozart. For each composition in the training set, the sys-
tem computed the values of 20 features, most of which are properties of
counterpoint.
26
Other features included the stability of the duration of
successive time intervals between two changes in the music, and the frac-
tion of bars that begin with a dissonant sonority.
27
Van Kranenburg and
Backer experimented with different sets of features, with results ranging
from 64 percent success up to 94 percent. This area of research is still,
at the time of writing, very much in its infancy. But with the increasing
26
Counterpoint is the technique of combining two or more melodies in such a way that they
establish a harmonic relationship.
27
A dissonant sonority is an inharmonius sound.
