Exercises
Problem 1. Diagonalize (if possible) the following matrices:
2 0 −1
(a) A = 0 1 0 ;
0 0 −1
2 0 −1
(b) A = 0 1 0 .
0 0 1
1 0 −1
Problem 2. Find the eigenvalues and eigenvectors of the matrix A = 0 0 0 . Then, determine
−1 0 1
an orthonormal matrix P such that PT AP is diagonal.
Problem 3. Using the Gauss elimination method, determine the solutions of the system
x + y + 4z = 2
x + 2y + 3z = 3
2x + 4y − z = 1
Problem 4. Using the Gauss elimination method, determine the solutions of the system
x+y−z =0
2x + y + 3z = 1
3x + 2y + 2z = 2
Problem 5. Using the Gauss elimination method, determine the solutions of the system
x+y−z =0 perche non si fa la scala
2x + y + 3z = 1 anche in R4
3x + 2y + 2z = 1
Problem 6. Determine the sign of the quadratic form q(x) = xT Hx in the following cases:
2 1
(a) H = ;
1 4
−2 0 2
(b) H = 0 4 1 ;
2 1 1
1 0 3
(c) H = 0 2 2 .
3 2 20
Problem 7. Determine the Cholesky decomposition of the following matrix:
6 1
H= .
1 4
" √ #
6 q0
T
Solution. H = LL with L = . ■
√1 23
6 6
Problem 8. Let us consider the following vectors of R3 :
1 0
v1 = 0 , v2 = 1
1 1
and denote by W the subspace of R3 generated by v1 , v2 . Determine an orthonormal basis of W .
1
Problem 9. Let us consider the following vectors of R4 :
2 0 1
0 1 1
v1 = 2 , v2 = 1 , v3 = 0
,
2 0 0
and denote by W the subspace of R4 generated by v1 , v2 , v3 . Determine an orthonormal basis of W .
0 1
Problem 10. Let A = 1 1 . Determine the Moore-Penrose pseudo-inverse of A.
0 1