use latex to set the label of the axis

plt.xlabel("$x_1$")

plt.ylabel("$x_2$")

import numpy as np
import matplotlib.pyplot as plt

from sklearn.decomposition import PCA, KernelPCA
from sklearn.datasets import make_circles


np.random.seed(0)


'''what's the meaning of the codes as follow??'''
reds = y == 0
blues = y == 1

plt.plot(X[reds, 0], X[reds, 1], "ro")
plt.plot(X[blues, 0], X[blues, 1], "bo")