Why define b1_1 as np.array in video Forward prop in a single layer

Course Q&A Machine Learning Specialization Advanced Learning Algorithms
1

b1_1, b1_2, b1_3 are defined as np.array instead of plain number, and calculating z in the next line by adding b.

Maybe the following code is more reasonable:

x = np.array([200, 17])
w1_1 = np.array([1, 2])
b1_1 = -1
z1_1 = np.dot(w1_1, x) + b1_1

2

Your code can’t be vectorized if we want to compute all of the layer outputs efficiently.