docs: add some documentation in the function _get_convol_img_fn

ot/bregman/_convolutional.py

@@ -21,7 +21,9 @@
 
 
 def _get_convol_img_fn(nx, width, height, reg, type_as, log_domain=False):
-    """Return the convolution operator for 2D images. The function constructed is equivalent to blurring on horizontal then vertical directions."""
+    """Return the convolution operator for 2D images.
+
+    The function constructed is equivalent to blurring on horizontal then vertical directions."""
     t1 = nx.linspace(0, 1, width, type_as=type_as)
     Y1, X1 = nx.meshgrid(t1, t1)
     M1 = -((X1 - Y1) ** 2) / reg
@@ -30,11 +32,13 @@ def _get_convol_img_fn(nx, width, height, reg, type_as, log_domain=False):
     Y2, X2 = nx.meshgrid(t2, t2)
     M2 = -((X2 - Y2) ** 2) / reg
 
+    # As M1 and M2 are computed first, we can use them to compute the convolution in log-domain
     def convol_imgs(log_imgs):
         log_imgs = nx.logsumexp(M1[:, :, None] + log_imgs[None], axis=1)
         log_imgs = nx.logsumexp(M2[:, :, None] + log_imgs.T[None], axis=1).T
         return log_imgs
 
+    # If normal domain is selected, we can use M1 and M2 to compute the convolution
     if not log_domain:
         K1, K2 = nx.exp(M1), nx.exp(M2)