# Listing 1
import numpy as np
import matplotlib.pyplot as plt
from sklearn import linear_model
import sklearn.metrics as metrics

x=np.arange(1,51)
y=np.zeros(50)
y[25:50]=1
plt.scatter(x.ravel(), y, color='black', zorder=10)
plt.ylabel('y')
plt.xlabel('X')
plt.ylim(-.25, 1.25)
plt.xlim(0, 51)
plt.show()