Matplotlib动画（三）：慢车与快车相向而行

本文主要使用Python和Matplotlib制作动画，动态演示初中数学中的慢车与快车相向而行的问题。

本文使用的软件：

• Python 3.8.8
• Matplotlib 3.3.4
• PyCharm 2018.3.3（Community Edition）

---

1 题目

一辆慢车从甲地匀速行驶至乙地，一辆快车同时从乙地匀速行驶至甲地，两车之间的距离y(km)与行驶时间t(h)之间的对应关系如图所示，当两车相距300km时，x的值是多少？

 2 动画源代码

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

pointA = 0
pointB = 600
xdata, ydata = [], []
speedA = 60
speedB = 90
frame_move = np.arange(0, 10 + 0.1, 0.1)

fig, axes = plt.subplots(nrows=1, ncols=2, figsize=(8, 4))
plt.rc('font', family='Times New Roman', size=9)

plt.title('慢车与快车相向而行', fontfamily='SimHei')
dot_a, = axes[0].plot([], [], 'bo')
dot_b, = axes[0].plot([], [], 'ro')
text_a = axes[0].text(pointA, -5, '慢车', fontfamily='KaiTi')
text_b = axes[0].text(pointB, -5, '快车', fontfamily='KaiTi')
line_distance, = axes[1].plot([], [], 'r-')
text_distance = axes[1].text(3, 500, '')


def init_graph():
    # print('init frame')
    axes[0].text(0, 20,
    '''
一辆慢车从甲地匀速行驶至乙地，一辆
快车同时从乙地匀速行驶至甲地，两车
之间的距离y（km）与行驶时间t(h)之
间的对应关系如图所示，当两车相距
300km时，x的值是多少？(@猴小萌)''', fontfamily='FangSong', fontsize=10)
    axes[0].plot([pointA, pointA, pointB, pointB], [2, 0, 0, 2], 'k-')
    axes[0].text(pointA, -5, '甲地', fontfamily='KaiTi')
    axes[0].text(pointB, -5, '乙地', fontfamily='KaiTi')

    axes[0].set_xlim(-100, 700)
    axes[0].set_ylim(-30, 70)
    axes[0].set_xticks([])
    axes[0].set_yticks([])
    axes[0].set_frame_on(False)

    axes[1].plot([0, 10], [300, 300], 'g--')
    axes[1].set_xlim(0, 10)
    axes[1].set_ylim(0, 800)
    axes[1].set_xticks((0, 4, 10))
    axes[1].set_yticks((300, 600))
    axes[1].set_xlabel('时间（h）', fontfamily='KaiTi')
    axes[1].set_ylabel('距离（Km）', fontfamily='KaiTi')


def animate(t):
    # print(t)
    x_a, x_b = 0, 0

    if t == 0:
        xdata.clear()
        ydata.clear()

    x_a = pointA + speedA * t
    if x_a > pointB:
        x_b = pointB
    dot_a.set_data(x_a, 0)
    text_a.set_position((x_a, 5))

    x_b = (pointB - pointA) - speedB * t
    if x_b <=0:
        x_b = 0
    dot_b.set_data(x_b, 0)
    text_b.set_position((x_b, 5))

    xdata.append(t)
    ydata.append(abs(x_b - x_a))
    line_distance.set_data(xdata, ydata)
    text_distance.set_text('x: {:>4.1f}\ny: {:>4.1f}'.format(t, abs(x_b - x_a)))
    #return dot_a, dot_b, text_a, text_b, line_distance, text_distance


ani = animation.FuncAnimation(fig, animate, frames=frame_move, init_func=init_graph, interval=200, repeat=False)
ani.save('慢车与快车相向而行.gif')
plt.show()