Matrix Operation Exercises
Exercises
 Suppose
X
is a matrix in R. Which of the following is not equivalent toX
? A)
t( t(X) )
 B)
X %*% matrix(1,ncol(X) )
 C)
X*1
 D)
X%*%diag(ncol(X))
 A)

Solve the following system of equations using R:
What is the solution for $$c$?

Load the following two matrices into R:
a < matrix(1:12, nrow=4) b < matrix(1:15, nrow=3)
Note the dimension of
a
and the dimension ofb
.In the question below, we will use the matrix multiplication operator in R,
%*%
, to multiply these two matrices.What is the value in the 3rd row and the 2nd column of the matrix product of
a
andb
? 
Multiply the 3rd row of
a
with the 2nd column ofb
, using the elementwise vector multiplication with*
.What is the sum of the elements in the resulting vector?