Book Image

NumPy: Beginner's Guide

By : Ivan Idris
Book Image

NumPy: Beginner's Guide

By: Ivan Idris

Overview of this book

Table of Contents (21 chapters)
NumPy Beginner's Guide Third Edition
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
NumPy Functions' References
Index

Time for action – creating a matrix from other matrices


We will create a matrix from two smaller matrices as follows:

  1. First, create a 2-by-2 identity matrix:

    A = np.eye(2)
    print("A", A)

    The identity matrix looks like the following:

    A [[ 1.  0.]
     [ 0.  1.]]
    
  2. Create another matrix like A and multiply it by 2:

    B = 2 * A
    print("B", B)

    The second matrix is as follows:

    B [[ 2.  0.]
     [ 0.  2.]]
    
  3. Create the compound matrix from a string. The string uses the same format as the mat() function—use matrices instead of numbers:

    print("Compound matrix\n", np.bmat("A B; A B"))

    The compound matrix is shown as follows:

    Compound matrix
    [[ 1.  0.  2.  0.]
     [ 0.  1.  0.  2.]
     [ 1.  0.  2.  0.]
     [ 0.  1.  0.  2.]]
    

What just happened?

We created a block matrix from two smaller matrices with the bmat() function. We gave the function a string containing the names of matrices instead of numbers (see bmatcreation.py):

from __future__ import print_function
import numpy as np

A = np.eye(2)
print("A", A)
B = 2 * A
print("B...