Slicing using vectors

[paul18fr]

Hi all

Does somebedoy know how to use vectors for slicing (see code herebellow)?

I got the following error "only integer scalar arrays can be converted to a scalar index" but I do not understand since I'm using a scalar (numpy) array, or I'm missing something

Thanks

Paul

n = 100
m = 2
A = np.random.randint(66, size=(n,m), dtype=np.int32)
i = np.random.randint(n-4, size=int(0.5*n), dtype=np.int32)
j = i + 4*np.ones(int(0.5*n), dtype=np.int32)
extract1_A = A[i,:]     # as usual = OK
#extract2_A = A[i:i+4,:] # fails
extract3_A = A[i:j,:] # fails