Matrix-Matrix Calculations

Linear Algebra for Data Science in R

Eric Eager

Data Scientist at Pro Football Focus

Matrix-Matrix Multiplication Motivations

Linear Algebra for Data Science in R

How Matrix Multiplication Works

Linear Algebra for Data Science in R

How Matrix Multiplication Works

A%*%B

     [,1] [,2]
[1,]    2    5
[2,]    1    4

B%*%A

     [,1] [,2]
[1,]    2    1
[2,]    5    4

A*B

     [,1] [,2]
[1,]    0    2
[2,]    2    2
Linear Algebra for Data Science in R

The Identity Matrix

Linear Algebra for Data Science in R

The Identity Matrix

print(A)

     [,1] [,2]
[1,]    1    2
[2,]    2    1

I <- diag(2)
print(I)

     [,1] [,2]
[1,]    1    0
[2,]    0    1

I%*%A

     [,1] [,2]
[1,]    1    2
[2,]    2    1

A%*%I

     [,1] [,2]
[1,]    1    2
[2,]    2    1
Linear Algebra for Data Science in R

Additional Importance Concepts for Matrices

  1. Square Matrices

  2. The Matrix Inverse

  3. Singular Matrices

  4. Diagonal and Triangular Matrices

Linear Algebra for Data Science in R

Let's practice!

Linear Algebra for Data Science in R

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