certain animal aggregations has been widely discussed (3). RCD may also be 
computed by a sequence of simple arithematic operations as follows: 
(a) *SPLIT BUGS.PA BUGS.X BUGS.Y 
(b) *CDIF BUGS.X BUGS.DX 
(c) *CDIF BUGS.Y BUGS.DY 
(d) UCTAN BUGS.DX BUGS.DY BUGS.DI 
(e) *CDIF BUGS.DI BUGS.AC 
(0 *MULT/CO BUGS.AC BUGS.AV nl 
(g) *ABSV BUGS.AV BUGS.RD 
Where “CDIF” is the CENTRAL DIFFERENCE operator (a discrete 
approximation to the differential operator), “CTAN” is the CONTINUOUS 
ARCTANGENT operator, “MULT/CO” denotes multiplication by a constant 
and “ABSV” is the ABSOLUTE VALUE operator. The resultant “BUGS.DI” 
of step (d) is the direction of travel measured in degrees with respect to the 
Bugsystem reference frame; it could have been generated from the original path 
data using the DIRECTION OF TRAVEL operator. The resultant “BUGS.AV” 
of step (e) contains angular velocities (measured in degrees per second); this file 
could have been produced using the ANGULAR VELOCITY operator. Other 
operators have been developed to evaluate LINEAR VELOCITY and NET TO 
GROSS DISPLACEMENT RATIO functions defined upon path data. 
Simple Statistical Processing 
For the purpose of statistical analysis two different types of data 
structure—representing two levels in a structural hierarchy-may be 
distinguished as “samples”: vectors and files. Many statistical operators 
recognize this distinction. For example the STATISTICAL PARAMETER 
operator estimates parameters such as the mean, variance, standard deviation, 
skewness, kurtosis, etc. The command 
*STAT/VE BUGS.LV BUGS.ST 
produces the resultant file “BUGS.ST’, containing one data vector (i.e., a list 
of statistical parameters) for each data vector in the operand, whereas the 
command 
*STAT/FI BUGS.LV BUGS.ST 
produces only one resultant data vector characterizing the entire file. In either 
case, the user can LIST the resultant parameters. Similarly, the SLOT operator 
provides for estimation of density and distribution functions via histograms 
both for individual vectors and entire files. These data may be displayed 
graphically (Figure 16-3) or LISTed on the terminal or the line printer. 
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