import numpy as np
import pylab as pl

def f(x):
    return x**2 - (3 * x) - 50

# Improve this function by adding parameters.
# For example, pass in the range limit as well as the first
# two parameters into linspace.
def points():
    i = 0
    a = np.linspace(-10., 10., 10)
#   b = np.arange(10)
    b = np.zeros(10)
    while i < 10:
        b[i] = f(a[i])
        i = i + 1
    return a, b

x, y = points()

pl.plot(x, y)

# I showed how to create a function (points) and use it in this context.
# However, we could have easily accomplished the same by simply doing
#
#        pl.plot(x, f(x))
#
# without creating the function.

pl.show()