#
# conv. example
# 
import numpy as np

ind  = np.array([[1,2,3,4],
                 [4,3,2,1],
                 [0,1,2,3],
                 [3,2,1,2]])
filt = np.array([[1,0,2],
                 [0,2,0],
                 [1,1,-1]])
outd = np.zeros((2,2))

for i in range(2):
  for j in range(2):
    outd[i][j] = np.sum(ind[i:i+3,j:j+3]*filt)

print(outd)