Doing Math in R Part 2

 1.  Finding the sum and difference of these two matrices. 

A = matrix(c(2,0,1,3), ncol=2) and B = matrix(c(5,2,4,-1), ncol=2)


a) Find A + B

First, assign the matrices to a value, then assign a new value to represent the sum of both matrices. Run that value to get the new matrix of A + B.

A <- matrix(c(2,0,1,3), ncol=2)

B <- matrix(c(5,2,4,-1), ncol=2)

AB_sum <- A + B

AB_sum

Result:

     [,1] [,2]

[1,]    7    5

[2,]    2    2 


b) Find A - B

First, assign the matrices to a value, then assign a new value to represent the difference between the two matrices. Run that value to get the new matrix of A - B.

A <- matrix(c(2,0,1,3), ncol=2)

B <- matrix(c(5,2,4,-1), ncol=2)

AB_dif <- A - B

AB_dif

Result:

     [,1] [,2]

[1,]   -3   -3

[2,]   -2    4 


2.  Using the diag() function to build a matrix of size 4 with the following values in the diagonal 4,1,2,3.

I assigned the four numbers to a vector C, then, using the diag() function, it automatically creates a matrix with those numbers as the diagonal values.

C <- c(4,1,2,3)

diag(C)

Result:

     [,1] [,2] [,3] [,4]

[1,]    4    0    0    0

[2,]    0    1    0    0

[3,]    0    0    2    0

[4,]    0    0    0    3 


3. Generate the following matrix:

## [,1] [,2] [,3] [,4] [,5]
## [1,] 3 1 1 1 1
## [2,] 2 3 0 0 0
## [3,] 2 0 3 0 0
## [4,] 2 0 0 3 0

## [5,] 2 0 0 0 3 


I created a matrix D using the diag() function to make it 5 x 5 and have all the diagonal values equal to 3. Then, I needed to update the values in row 1, columns 2 through 5, to equal 1 and update the values in column 1, rows 2 through 5, to equal 2. Running D at the end gives me the new updated matrix.

D <- diag(x = 3, nrow = 5, ncol = 5)

D[1, 2:5] <- 1

D[2:5, 1] <- 2

D

Result:

     [,1] [,2] [,3] [,4] [,5]

[1,]    3    1    1    1    1

[2,]    2    3    0    0    0

[3,]    2    0    3    0    0

[4,]    2    0    0    3    0

[5,]    2    0    0    0    3 




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