To sum elements along a specific axis in a multi-dimensional array, you can set the axis parameter of numpy.sum() to the desired axis. For example, to sum elements vertically (column-wise) in a 2-D array: import numpy as np arr = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) column_sums = np.sum(arr, axis=0) print(column_sums)