# coding: utf-8 # # numpy: Broadcasting # In[1]: import numpy as np # In[2]: a = np.arange(9).reshape(3, 3) print(a.shape) print(a) b = np.arange(4, 4+9).reshape(3, 3) print(b.shape) print(b) # In[3]: a+b # So this is easy and one-to-one. # # --- # # What if the shapes do not match? # In[4]: a = np.arange(9).reshape(3, 3) print(a.shape) print(a) b = np.arange(3) print(b.shape) print(b) # What will this do? # In[5]: a+b # It has *broadcast* along the last axis! # --- # # Can we broadcast along the *first* axis? # In[6]: a+b.reshape(3, 1) # Rules: # # * Shapes are matched axis-by-axis from last to first. # * A length-1 axis can be *broadcast* if necessary.