如何在matplotlib的stackplot中显示负值？

import matplotlib.pyplot as plt
import numpy as np

# 创建数据
x = np.arange(5)
y1 = np.array([1, 2, -3, 4, 5])
y2 = np.array([2, -1, 3, -2, 1])

# 设置绘图参数
fig, ax = plt.subplots()
ax.set_title('Stackplot with Negative Values')
ax.set_xlabel('X')
ax.set_ylabel('Y')

# 调整数据
y1_pos = np.maximum(y1, 0)
y1_neg = np.minimum(y1, 0)
y2_pos = np.maximum(y2, 0)
y2_neg = np.minimum(y2, 0)

# 使用stackplot绘制图形
ax.stackplot(x, y1_pos, y1_neg, labels=['Positive', 'Negative'])
ax.stackplot(x, y2_pos, y2_neg, labels=['Positive', 'Negative'])

# 添加图例
ax.legend(loc='upper left')

plt.show()