如何在Matplotlib中编写分段函数乳胶代码？

Question

我想在matplotlib分段表达这样的传奇节写：

\[f(x) = \left\{ 
    \begin{array}{lr} 
    x^2 & : x < 0\\ 
    x^3 & : x \ge 0 
    \end{array} 
\right. 
\] 

问题是Matplotlib不承认\开始\结束\等等。 谢谢

Answer 1

好的，这里是解决方案。它包括加载乳胶mathsymbols包。它假设你已经在PC中安装了所需的乳胶包。在​​

代码的更多信息：

#/usr/bin/env python3 
# -*- coding: utf-8 -*- 


import numpy as np 
import matplotlib.pyplot as plt 
from matplotlib import rcParams 


rcParams['text.latex.unicode'] = True 
rcParams['text.usetex'] = True 
rcParams['text.latex.preamble'] = '\usepackage{amsthm}', '\usepackage{amsmath}', '\usepackage{amssymb}', 
'\usepackage{amsfonts}', '\usepackage[T1]{fontenc}', '\usepackage[utf8]{inputenc}, \usepackage{multicol}' 
rcParams['legend.handleheight'] = 3.0 
#This fixes the legend line be placed at same height that text legend 


def f(x): 
    return np.piecewise(x, [x < 2.0, x > 2.0], [lambda x: x ** 2.0, lambda x: 4.0]) 


fig, ax = plt.subplots() 
x = np.linspace(-5.0, 5.0, 1000) 
ax.axis([x[0], x[-1], x[0], x[-1]]) 
ax.spines['left'].set_position('center') 
ax.spines['right'].set_color('none') 
ax.spines['bottom'].set_position('center') 
ax.spines['top'].set_color('none') 
ax.spines['left'] 
ax.spines['bottom'] 
ax.xaxis.set_ticks_position('bottom') 
ax.yaxis.set_ticks_position('left') 
ticks = [] 
for i in range(int(x[0]), int(x[-1] + 1), 1): 
    ticks.append(i) 
ticks.remove(0) 
ax.set_xticks(ticks) 
ax.set_yticks(ticks) 
ax.plot(x, f(x), 'b-', 2, 4, 'wo', markeredgecolor='b', 
     markerfacecolor='w', lw=2.0) 
tlegend = r'$f(x)=\left\{\begin{array}{lr} x^2 & : x<2\\ 4 & : x>2\end{array}\right\}$' 
ax.legend([tlegend], loc='lower right') 
ax.set_title(ur'$Función\; A\; Trozos$') # If you use accents put ur option. 
ax.grid('on') 
plt.show() 

图像：

如果有人知道如何改进下面的代码将受到欢迎：

rcParams['legend.handleheight'] = 3.0 
#This fixes the legend line be placed at same height that text legend