Question

I have a numpy array A of shape(N,2) and a numpy array S of shape(N).

How do I multiply both arrays? Currently I am using this code:

tupleS = numpy.zeros( (N , 2) )
tupleS[:,0] = S
tupleS[:,1] = S
product = A * tupleS

I am a python beginner. Is there a better way to do this?

Answer 1

Numpy uses row-major order, so you have to explicitly create a column. As in:

>> A = numpy.array(range(10)).reshape(5, 2)
>>> B = numpy.array(range(5))
>>> B
array([0, 1, 2, 3, 4])
>>> A * B
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: shape mismatch: objects cannot be broadcast to a single shape
>>> B = B.reshape(5, 1)
>>> B
array([[0],
       [1],
       [2],
       [3],
       [4]])
>>> A * B
array([[ 0,  0],
       [ 2,  3],
       [ 8, 10],
       [18, 21],
       [32, 36]])