I want write in the legend section of matplotlib a piecewise expression like this:
\[f(x) = \left\{ \begin{array}{lr} x^2 & : x < 0\\ x^3 & : x \ge 0 \end{array} \right. \] The problem is Matplotlib not recognize \begin \end \ and so on. Thanks
41 Answer
Ok, here is the solution. It consists to load the latex mathsymbols packages. It supposes that you have installed the required latex packages in your PC. More information in MatplotlibRC
The code:
#/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() An Image:
If somebody knows how to improve the code below it will be welcome:
rcParams['legend.handleheight'] = 3.0 #This fixes the legend line be placed at same height that text legend 
