def distance(a, b):
return (np.sum((a - b)**<NUM_LIT:2>))**<NUM_LIT:0.5><EOL>
Return the distance between two vectors (points) a and b.

Parameters
----------
a : numpy.ndarray
    First vector.
b : numpy.ndarray
    Second vector.

Returns
-------
numpy.float64
    A distance between two vectors (points).