ValueError:参数U的大小为4，与箭头位置数1不匹配

Question

代码：

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import colors
import math as mt
from numpy import linalg as LA
from mpl_toolkits.mplot3d import Axes3D
from sklearn.datasets import fetch_olivetti_faces
%matplotlib inline

x=np.array([1,0]) # Original vector
theta = 30 * mt.pi / 180 # 30 degress in radian
A = np.array([[np.cos(theta), -np.sin(theta)],[np.sin(theta), np.cos(theta)]]) # Rotation matrix for theta=30 degrees
B = np.array([[3,0],[0,1]]) # Stretching matrix

Ax = A @ x  # y1 is the rotated vector
Bx = B @ x  # y2 is the stretched vector

# Reshaping and storing both x and Ax in t1 to be plotted as vectors
t1 = np.concatenate([x.reshape(1,2), Ax.reshape(1,2)])
# Reshaping and storing both x and Bx in t2 to be plotted as vectors
t2 = np.concatenate([x.reshape(1,2), Bx.reshape(1,2)])

# origin point
x_pos = 0
y_pos = 0

fig, ax = plt.subplots()


# Plotting t1
ax1.quiver(x_pos, y_pos, t1[:,0], t1[:,1], color=['b', 'g'], width=0.013, angles='xy', scale_units='xy', scale=1)
ax1.set_xlabel('x', fontsize=14)
ax1.set_ylabel('y', fontsize=14)
ax1.set_xlim([-0.5,1.5])
ax1.set_ylim([-0.5,1])
ax1.set_aspect('equal')
ax1.grid(True)
ax1.set_axisbelow(True)
ax1.set_title("Rotation transform")
ax1.axhline(y=0, color='k')
ax1.axvline(x=0, color='k')
ax1.text(1, 0.1, "$\mathbf{x}$", fontsize=16)
ax1.text(0.8, 0.6, "$\mathbf{Ax}$", fontsize=16)


plt.show()

我试图在转换后用python和jupyter笔记本绘制向量。我是新来的。我的代码在使用ax1.quiver方法后给出了错误消息。

错误消息：

ValueError                                Traceback (most recent call last)
<ipython-input-20-f96b87a2142a> in <module>
     29 
     30 # Plotting t1
---> 31 ax1.quiver(x_pos, y_pos, t1, t1, color=['b', 'g'], width=0.013, angles='xy', scale_units='xy', scale=1)
     32 ax1.set_xlabel('x', fontsize=14)
     33 ax1.set_ylabel('y', fontsize=14)

~/python-project/linear-algebra/py3env/lib/python3.7/site-packages/matplotlib/__init__.py in inner(ax, data, *args, **kwargs)
   1436     def inner(ax, *args, data=None, **kwargs):
   1437         if data is None:
-> 1438             return func(ax, *map(sanitize_sequence, args), **kwargs)
   1439 
   1440         bound = new_sig.bind(ax, *args, **kwargs)

~/python-project/linear-algebra/py3env/lib/python3.7/site-packages/matplotlib/axes/_axes.py in quiver(self, *args, **kw)
   5019         args = self._quiver_units(args, kw)
   5020 
-> 5021         q = mquiver.Quiver(self, *args, **kw)
   5022 
   5023         self.add_collection(q, autolim=True)

~/python-project/linear-algebra/py3env/lib/python3.7/site-packages/matplotlib/quiver.py in __init__(self, ax, scale, headwidth, headlength, headaxislength, minshaft, minlength, units, scale_units, angles, width, color, pivot, *args, **kw)
    501                                              **kw)
    502         self.polykw = kw
--> 503         self.set_UVC(U, V, C)
    504         self._initialized = False
    505 

~/python-project/linear-algebra/py3env/lib/python3.7/site-packages/matplotlib/quiver.py in set_UVC(self, U, V, C)
    574         for name, var in zip(('U', 'V', 'C'), (U, V, C)):
    575             if not (var is None or var.size == self.N or var.size == 1):
--> 576                 raise ValueError(f'Argument {name} has a size {var.size}'
    577                                  f' which does not match {self.N},'
    578                                  ' the number of arrow positions')

ValueError: Argument U has a size 4 which does not match 1, the number of arrow positions

我搜索了谷歌的这种错误信息，但我没有找到任何有用的解决方案。我不明白什么信息告诉我要改正。

Answer 1

回滚到matplotlib=3.1.1将显示您的向量图。

对于conda：

conda remove matplotlib
conda install matplotlib=3.1.1

注意:在笔记本中，您可能会看到下面的错误与您的情节(但这不会影响您的代码)。

/site-packages/matplotlib/mpl-data/stylelib/_classic_test_patch.mplstyle.中第4行的坏键"text.kerning_factor“

只需转到该文件并注释掉第4行。请参见下面的回答：

因素“

Answer 2

因此，我不确定您是否使用了不支持t1[:,0]表示法的较旧版本或更新版本的quiver，但它所期望的是每个t1的值。

ax1.quiver(x_pos, y_pos, t1[0,0], t1[0,1], color=['b','g'], width=0.013, angles='xy', scale_units='xy', scale=1)
ax1.quiver(x_pos, y_pos, t1[1,0], t1[1,1], color=['b','g'], width=0.013, angles='xy', scale_units='xy', scale=1)

这可以通过更改quiver版本来解决。

Answer 3

根据多古，x_pos和y_pos必须用[] (即[x_pos, y_pos])括起来。我使用matplotlib 3.3.2，它可以工作。