from mpl_toolkits.mplot3d import axes3d
import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()
ax = fig.gca(projection='3d')

# Make the grid
x, y, z = np.meshgrid(np.array([1]),
                      np.array([1]),
                      np.array([1]))   #起點(1, 1, 1)

# Make the direction data for the arrows
u = np.array([2])
v = np.array([4])
w = np.array([5])    # 方向(2, 4, 5)

ax.quiver(x, y, z, u, v, w, length=1, normalize=True) # 模長1
ax.set_xlim(0, 2)
ax.set_ylim(0, 2)
ax.set_zlim(0, 2)
plt.show()