Exercise

Repeat the additional exercise from the matrices chapter and pay attention to the differences.

1. Create in Mata
   • a scalar a that contains the number 2,
   • a matrix A with 4 rows and 4 columns and all the elements being 2, and
   • a matrix B of the same dimension, which has the value 2 on the diagonal and 0 otherwise.
   Display scalar a, matrix A and matrix B.
2. Do the following computations in Mata:
   • Multiply the scalar a with matrix A and store the result in matrix C
   • Calculate the sum of matrix C and the inverse of matrix B and store it in matrix D
   • Combine matrices A, B, C and D into one 8x8 matrix E
   • Create a vector b that contains the first, third and fifth element of the first row of E
   Display matrix C, matrix D, matrix E and vector b.
Implement the following exercise using as many Mata shortcuts as possible.
3. Add 20 rows to matrix A with the following values:
   • In column 1, start with the value 1 in the first new row and increase in increments of 1 to the value 20, the second column starts with the value 2 and increases in increments of 1 to the value 21, the third column starts with the value 3 and increases in increments of 1 to the value 22 and the fourth column starts with the value 4 and increases in increments of 1 to the value 23.
   • Display the entire 12th row
   • Display the second to fourth column in the last five rows
   • Create a selection vector s, which has as many rows as A, the value 1 in rows 2, 12 and 14 and zeros otherwise
   • Display all rows of matrix A, for which vector s is 1
   • Display all columns of matrix A, for which the value in row 7 is smaller than 5