'''Experimental plots of sequences'''
import numpy as np
import matplotlib.pyplot as plt

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = 1 + (-1)**n/float(n)
plt.figure(1)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, -0.1, 1.6])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = np.arctan(n)
plt.figure(2)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, 0.7, 1.6])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = np.arctan(n) + 3*(-1)**n/float(n)
plt.figure(3)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, -3, 3])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = np.arctan(n) + (-1)**n
plt.figure(4)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, -0.5, 3.0])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = np.arctan(n) + 2.0/n**2
plt.figure(5)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, 1.4, 2.9])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = np.cos(n*np.pi)
plt.figure(6)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, -1.2, 1.2])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = n**2
plt.figure(7)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, -10, 910])
plt.grid()  

a = np.zeros(30)
for n in range(1,31):
  a[n-1] = (-1)**n*n
plt.figure(8)
plt.plot(range(1,31),a,'*')
plt.axis([0, 31, -31, 31])
plt.grid()  

plt.show()