练习利用matplotlib库画三维曲面图、雷达图等

`matplotlib`是一个强大的数据可视化库，用于Python，它支持创建各种类型的图表，包括三维图形。下面我会简单讲解如何使用`matplotlib`及其姐妹库`mpl_toolkits.mplot3d`来绘制三维曲面图和雷达图。

**三维曲面图**:
要绘制三维曲面图，你需要先导入`matplotlib.pyplot`和`mpl_toolkits.mplot3d`模块，然后创建一个`Axes3D`对象。这里以绘制一个简单的二维函数z=f(x,y)为例：

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

# 定义x和y网格
x = np.linspace(-5, 5, 100)
y = np.linspace(-5, 5, 100)
X, Y = np.meshgrid(x, y)

# 定义函数z = x^2 + y^2
Z = X**2 + Y**2

# 创建3D图像
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.plot_surface(X, Y, Z, cmap='viridis')  # 使用颜色映射

ax.set_xlabel('X Label')
ax.set_ylabel('Y Label')
ax.set_zlabel('Z Label')

plt.show()

**雷达图**:
雷达图是一种用于比较多维度数据的特殊形式的折线图。首先需要`matplotlib.ticker`和`matplotlib.collections`。以下是如何制作雷达图的例子：

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.path import Path
from matplotlib.patches import PathPatch

def radar_factory(n):
    d = np.array([0] * n)
    angles = [2*np.pi*i/n for i in range(n)]
    codes = [(Path.MOVETO, (0,0))] + [(Path.LINETO, point) for point in zip(np.cos(angles), np.sin(angles))]
    path = Path(codes)
    return path, angles

def plot_radar(ax, angles, values, labels=None, **kwargs):
    if labels is None:
        labels = ['Dim {}'.format(i+1) for i in range(len(values[0]))]
    
    path, angles = radar_factory(len(values))
    patch = PathPatch(path, facecolor='w', edgecolor='k', lw=2)
    ax.add_patch(patch)

    ax.set_thetagrids(angles * 180/np.pi, labels, radius=1.1)
    ax.axis('equal')  # Equal aspect ratio ensures that circles are drawn as circles.
    ax.set_rlabel_position(90)  # Move radial labels away from plotted line

    # Plot data
    lines = ax.plot(angles * np.ones_like(values), values, **kwargs)
    ax.fill(angles * np.ones_like(values), values, alpha=0.25)

# 示例
values = [[4, 6, 7, 8, 5], [2, 3, 5, 7, 6]]
plot_radar(ax, angles=np.arange(5), values=values, label=['A', 'B'], linestyle='--', linewidth=2)

plt.title("Radar Chart")
plt.show()