### generate random data in a rectangle
##  (xmin,ymin) to (xmax,ymax)
##  
N = 250;  # number of pts.
del = 1;  # twice the margin
xmin = ymin = -10;
xmax = ymax = 10;

dx = xmax-xmin;
dy = ymax-ymin;

m = dy/dx;   # slope of the diagonal

d0 = dx-.5*del;
a0 = xmin-.5*del;
b0 = ymin-.5*del;
d1 = dx+.5*del;
a1 = xmin+.5*del;
b1 = ymin+.5*del;

yx = zeros(N,3);

for i = 1:N
 if rand > .5
  yx(i,1) = 1;
  yx(i,2) = xmin + d0*rand;
  y1x = m*(yx(i,2)-xmin) + b1;
  yx(i,3) = y1x + (ymax-y1x)*rand;
 else
  yx(i,1) = -1;
  yx(i,2) = a1 + d1*rand;
  y0x = m*(yx(i,2)-xmin) + b0;
  yx(i,3) = ymin + (y0x-ymin)*rand;
 endif
endfor