with XMIN, XMAX, YMIN, and YMAX denoting the minimum X value, the maximum X value, the minimum Y value, and the maximum Y value, respectively. The Xi and Yi mean the x or y coordinate corresponding to the minimum or maximum value.
where <y> is a variable containing the x-coordinates of the data points;
<x> is a variable containing the y-coordinates of the data points;
<yout> is a variable containing the y-coordinates of the extreme points;
<xout> is a variable containing the x-coordinates of the extreme points;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.
. Following data from Eddy's ACM article read x y 2.0 0.0 1.73 -1.0 1.0 1.73 0.0 2.0 0.1 0.1 -1.0 -1.73 0.2 -0.2 -1.73 1.0 -0.3 0.3 0.0 -2.0 -0.4 -0.4 -2.0 0.0 0.5 0.5 1.73 1.0 0.6 -0.6 -1.0 1.73 -0.7 0.7 -1.73 -1.0 -0.8 -0.8 1.0 -1.73 end of data . let y2 x2 = 2d convex hull y x let y3 x3 = extreme points y2 x2 let xtemp = x2(1) let ytemp = y2(1) let x2 = combine x2 xtemp let y2 = combine y2 ytemp . title case asis title offset 2 title Extreme Points of the Convex Hull y1label Y x1label X tic offset units screen tic offset 3 3 x3label . character hw 1 0.75 all character fill on all character color black black red character circle blank circle line blank solid blank . pre-sort off plot y x and plot y2 x2 and plot y3 x3 pre-sort on
Date created: 01/07/2013