#
# walker.py
#
# Plots 1D Random Walks
#
# Carlos Rocha - February 2005
##############################

from time import *
from numarray import *
from pylab import *

# Random Number Generator
##############################

class RandStep:
    def __init__(self):
       self.seed =  int(time()) # Initial Random Seed
    
    def next(self):
        """Returns a random step of size 1, using a LCG"""
        self.seed = (8121 * self.seed + 28411) % 134456
        if (self.seed > 67228):
            return 1
        else:
            return -1


# Random 1D Walker
##############################

def main() :
    pcount = 10    # Number of particles
    points = 1000  # Number of points

    rand = RandStep()

    ps = zeros((pcount,points))

    # Draw particles
    for i in range(pcount):
        for j in range(1,points):
            ps[i][j]=ps[i][j-1] + rand.next()
        plot(ps[i])

    # Draw errorbars
    for x in range(points/100):
        errorbar(x*100,0,yerr=3*sqrt(x*100))

    title("1D Random Walkers")
    axis([0, 1000, -70, 70])
    show()

if __name__ == "__main__" : main()