File:Relative neighborhood graph.svg

from pyx import canvas,path,color
from math import *
from random import seed,random
seed(12345)

npoints = 100
radius = 0.05
exclusion = 0.2     # prevent points from being too close
scale = 5
beta1 = 1.1
beta2 = 0.9
theta1 = asin(1/beta1)
theta2 = pi - asin(beta2)

def dist2(p,q):
    return (p[0]-q[0])**2 + (p[1]-q[1])**2

points = []
while len(points) < 100:
    p = (random()*scale,random()*scale)
    if points:
        nn = min(dist2(p,q)**0.5 for q in points)
        if nn < exclusion:
            continue
    points.append(p)

def neighbors(p,q):
    for r in points:
        if max(dist2(p,r),dist2(q,r)) < dist2(p,q):
            return False
    return True

c = canvas.canvas()

def edge(p,q):
    c.stroke(path.line(p[0],p[1],q[0],q[1]),
             [color.rgb.black])

def point(p):
    c.fill(path.circle(p[0],p[1],radius),[color.rgb.red])

for p in points:
    for q in points:
        if p < q and neighbors(p,q):
            edge(p,q)

for p in points:
    point(p)

c.writePDFfile("Relative_neighborhood_graph")