C21. Compute the product AB of the two matrices below using both the definition of the matrix-vector product (Definition MVP) and the definition of matrix multiplication (Definition MM)
a <- matrix(c(1, 3, 2, -1, 2, 1, 0, 1, 0), ncol = 3, byrow = T)
b <- matrix(c(4, 1, 2, 1, 0, 1, 3, 1, 5), ncol = 3, byrow = T)
a%*%b## [,1] [,2] [,3]
## [1,] 13 3 15
## [2,] 1 0 5
## [3,] 1 0 1