title: What is the behaviour of subplot given single argument?
body: <p><a href="https://docs.opencv.org/4.1.0/da/d6e/tutorial_py_geometric_transformations.html" rel="nofollow noreferrer">OpenCV.org</a> tutorial has the following example:</p>
  
  <pre><code>import numpy as np
  import cv2 as cv
  from matplotlib import pyplot as plt
  
  img = cv.imread('drawing.png')
  rows,cols,ch = img.shape
  
  pts1 = np.float32([[50,50],[200,50],[50,200]])
  pts2 = np.float32([[10,100],[200,50],[100,250]])
  
  M = cv.getAffineTransform(pts1,pts2)
  dst = cv.warpAffine(img,M,(cols,rows))
  plt.subplot(121),plt.imshow(img),plt.title('Input')
  plt.subplot(122),plt.imshow(dst),plt.title('Output')
  plt.show()
  </code></pre>
  
  <p>Here what is the role of <code>subplot()</code>? <a href="https://pythonspot.com/matplotlib-subplot/" rel="nofollow noreferrer">Docs</a> define it as,</p>
  
  <blockquote>
    <p>The Matplotlib subplot() function can be called to plot two or more
    plots in one figure. Matplotlib supports all kind of subplots
    including 2x1 vertical, 2x1 horizontal or a 2x2 grid.</p>
  </blockquote>
  
  <p>The provided examples have the arguments telling the height vs length ratio and the third argument is used as the index. But it is quite unhelpful in my case.</p>