a⃗ ⋅ b⃗ = |a⃗| |b⃗| cos∡(a⃗, b⃗)
|a⃗|, |b⃗| denote the lengths of the vectors.
∡(a⃗, b⃗) denotes the cosinus of the angle between the two vectors.
The following is valid :
a⃗ ⋅ b⃗ = a1b1 + a2b2 + a3c3
In NumPy:
>>> x = np.array([1,2,3])
>>> y = np.array([-7,8,9])
>>> np.dot(x,y)
36
>>>
dot can also be used for matrix multiplication.