## Exercises

1. In R we have vectors and matrices. You can create your own vectors with the function c.

 c(1,5,3,4)


They are also the output of many functions such as:

 rnorm(10)


You can turn vectors into matrices using functions such as rbind, cbind or matrix.

Create the matrix from the vector 1:1000 like this:

 X = matrix(1:1000,100,10)


What is the entry in row 25, column 3?

2. Using the function cbind, create a 10 x 5 matrix with first column x=1:10. Then add 2*x, 3*x, 4*x and 5*x to columns 2 through 5. What is the sum of the elements of the 7th row?

3. Which of the following creates a matrix with multiples of 3 in the third column?

• A) matrix(1:60,20,3)
• B) matrix(1:60,20,3,byrow=TRUE)
• C) x=11:20; rbind(x,2*x,3*x)
• D) x=1:40; matrix(3*x,20,2)