purpose of a sparse matrix python code example

Example: sparse matrix representation python use

import numpy as np
from scipy.sparse import csr_matrix

# create a 2-D representation of the matrix
A = np.array([[1, 0, 0, 0, 0, 0], [0, 0, 2, 0, 0, 1],\
 [0, 0, 0, 2, 0, 0]])
print("Dense matrix representation: \n", A)

# convert to sparse matrix representation 
S = csr_matrix(A)
print("Sparse matrix: \n",S)

# convert back to 2-D representation of the matrix
B = S.todense()
print("Dense matrix: \n", B)