matplotlib（3）-- legend（图例、说明、解释）,annotate(标注)，text（标注）

 1 import matplotlib.pyplot as plt
 2 import numpy as np
 3 
 4 x = np.linspace(-3, 3, 50)
 5 y1 = 2 * x + 1
 6 y2 = x ** 2
 7 
 8 plt.figure()
 9 l1, = plt.plot(x, y1, color = "red", linewidth = 5.0, linestyle = ‘--‘, label = ‘down‘)    #指定线的颜色, 宽度和类型
10 l2, = plt.plot(x, y2, label = "up")
11 
12 #给figure添加legend（图例、说明、解释）
13 plt.legend(handles = [l1, l2], labels = ["y1 = 2 * x + 1", "y2 = x ** 2"], loc = "best")
14 
15 plt.show()

 1 import matplotlib.pyplot as plt
 2 import numpy as np
 3 
 4 x = np.linspace(-3, 3, 50)
 5 y1 = 2 * x + 1
 6 X0 =1
 7 Y0 = 2 * X0 + 1
 8 
 9 #figure 1
10 plt.figure()
11 plt.plot(x, y1)
12 plt.scatter(X0, Y0, s = 30, color = ‘black‘)     #在数据线上画点
13 plt.plot([X0, X0], [Y0, 0], color = "black", linewidth = 3.0, linestyle = ‘--‘)       #过一点做垂直于X轴的垂线
14 
15 #坐标轴的移动 gca = “get current axis”
16 ax = plt.gca()
17 ax.spines["right"].set_color("none")
18 ax.spines["top"].set_color("none")
19 ax.xaxis.set_ticks_position("bottom")
20 ax.yaxis.set_ticks_position("left")
21 ax.spines["bottom"].set_position(("data", 0))   #Set the X and Y coordinates of the sprite simultaneously
22 ax.spines["left"].set_position(("data", 0))
23 
24 
25 #在figure上做标注的两种方法
26 #方法一
27 #关于annotate的相关参数介绍，参考博文 https://blog.csdn.net/leaf_zizi/article/details/82886755
28 ##########################
29 plt.annotate(r"$2*x_0 + 1 = %s$"%Y0, xy = (X0, Y0), xytext = (+30, -30),
30              textcoords = "offset points", fontsize = 16,
31              arrowprops = dict(arrowstyle = "->", connectionstyle = "arc3, rad=.2"))
32 #方法二
33 #补充：关于下角标的添加 “_+下角标字母”
34 #关于text的相关参数介绍，参考博文 https://blog.csdn.net/TeFuirnever/article/details/88947248
35 ##########################
36 plt.text(-3.7, 3, r"$This\ is\ y1 = 2 * x + 1\ \mu\ \sigma_i\ \alpha_t$",
37          fontdict={"size":16, "color":"red"})
38 
39 plt.show()