Conditional operations on numpy arrays
The problem is that you mask the receiving part, but do not mask the sender part. As a result:
c[(a > 3) & (b > 8)]+=b*2
# ^ 1x1 matrix ^3x4 matrix
The dimensions are not the same. Given you want to perform element-wise addition (based on your example), you can simply add the slicing to the right part as well:
c[(a > 3) & (b > 8)]+=b[(a > 3) & (b > 8)]*2
or make it more efficient:
mask = (a > 3) & (b > 8)
c[mask] += b[mask]*2
You can use numpy.where
:
np.where((a > 3) & (b > 8), c + b*2, c)
#array([[ 0, 18, 0, 0],
# [ 0, 0, 0, 0],
# [ 0, 0, 0, 0]])
Or arithmetically:
c + b*2 * ((a > 3) & (b > 8))
#array([[ 0, 18, 0, 0],
# [ 0, 0, 0, 0],
# [ 0, 0, 0, 0]])