Bug summary

matshow states that "(first dimension of the array) are displayed horizontally": https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.matshow.html#matplotlib-pyplot-matshow. However it seems that the first dimension is vertically.

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt


nx = 15
ny = 21

img = np.zeros((nx, ny))

for i in range(nx):
    for j in range(ny):
        if j == i:
            img[i, j] = 1

plt.figure()
plt.subplot(1, 2, 1)
plt.imshow(img)
plt.title('imshow')
plt.subplot(1, 2, 2)
plt.matshow(img, fignum=0)
plt.title('matshow')
plt.show()

Actual outcome

First dimension is shown vertically

Expected outcome

I would expect that the first dimension be show horizontally according to the documentation.

Additional information

No response

Operating system

Debian 12

Matplotlib Version

3.8.0

Matplotlib Backend

module://matplotlib_inline.backend_inline

Python version

3.10.12

Jupyter version

No response

Installation

conda