4_matrix_math.ipynb

Kernel: Python 3

import numpy as np

Calculate profit/loss from revenue and expenses

revenue = np.array([[180,200,220],[24,36,40],[12,18,20]])
expenses = np.array([[80,90,100],[10,16,20],[8,10,10]])

profit = revenue - expenses
profit

array([[100, 110, 120],
       [ 14,  20,  20],
       [  4,   8,  10]])

Calculate total sales from units and price per unit using matrix multiplication

price_per_unit = np.array([1000,400,1200])
units = np.array([[30,40,50],[5,10,15],[2,5,7]])

price_per_unit*units

array([[30000, 16000, 60000],
       [ 5000,  4000, 18000],
       [ 2000,  2000,  8400]])

In above case numpy is using broadcasting so it expands price_per_unit array from 1 row, 3 columns to 3 row and 3 columns. Correct way to do matrix multiplication is to use dot product as shown below

np.dot(price_per_unit,units)

array([34400, 50000, 64400])