from numpy import *
from matplotlib.pyplot import *

x0 = 100                      # initial amount
p = 5                         # interest rate
N = 40                         # number of years
index_set = range(N+1)
x = zeros(len(index_set))

"""
Alternative code, with p varying
randomly between 5 and 6:
p = ones(41)
p = p*5
p = p + random.rand(len(p))
"""

# Solution:
x[0] = x0
for n in index_set[1:]:
    x[n] = x[n-1] + (p/100.0)*x[n-1]
plot(x, 'ro')

xlabel('years')
ylabel('amount')
show()