###############
# Authored by Weisheng Jiang
# Book 4  |  From Basic Arithmetic to Machine Learning
# Published and copyrighted by Tsinghua University Press
# Beijing, China, 2022
###############

# Bk4_Ch1_03.py

import matplotlib.pyplot as plt
import numpy as np

x1 = np.linspace(-10, 10, num=201);
x2 = x1;

xx1, xx2 = np.meshgrid(x1,x2)
p = 2
zz = ((np.abs((xx1))**p) + (np.abs((xx2))**p))**(1./p)

fig, ax = plt.subplots(figsize=(12, 12))

ax.contour(xx1, xx2, zz, levels = np.arange(11), cmap='RdYlBu_r')

ax.axhline(y=0, color='k', linewidth = 0.25)
ax.axvline(x=0, color='k', linewidth = 0.25)
ax.set_xlim(-12, 12)
ax.set_ylim(-12, 12)
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
ax.spines['bottom'].set_visible(False)
ax.spines['left'].set_visible(False)
ax.set_xlabel('$x_1$')
ax.set_ylabel('$x_2$')
ax.set_aspect('equal', adjustable='box')
plt.show()