Using least squares, find the orthogonal projection of
u onto the subspace of R4
spanned by the vectors v1,
v2, and v3,
where
u = (6, 3, 9, 6), v1
= (2, 1, 1, 1), v2 = (1, 0, 1 ,1),
v3 = (-2, -1, 0, -1).
Problem 4. Let P be the orthogonal
projection associated with a closed subspace S in a
Hilbert space H, that is P is a linear operator
such that
P(f) = f if f ∈ S
and P(f) = 0 if f ∈ S⊥.
(a) Show that P2 = P and
P∗ = P.
(b) Conversely, if P is any bounded operator satisfying
P2 = P and P∗ = P,
prove that P is the orthogonal projection for some closed
subspace...
Prove that the least squares estimates in a simple linear
regression model are unbiased. Be sure to state carefully the
assumptions under which your proof holds.
2. (a). Prove that the sum of the two projection
operators is not a projection operator, unless the
multiplication of the two projection operators produces a zero
value.
(b). Prove that the result of the multiplication of two
projection operators is not a projection operator, unless
the two projection operators are hermitian.
Write a MATLAB code for discrete least squares trigonometric
polynomial S3(x), using m = 4 for f(x) = e^x * cos(2x) on the
interval [-pi, pi]. Compute the error E(S3).
(a) Find the matrix representation for the orthogonal projection
Pr : R 4 → R 4 onto the plane P= span
1
-1
-1
1
-1
-1
1
1
(b) Find the distance of vector ~y =
2
0
0
4
from the plane P.
Check the true statements below:
A. The orthogonal projection of y onto v is the same as the
orthogonal projection of y onto cv whenever c≠0.
B. If the columns of an m×n matrix A are orthonormal, then the
linear mapping x→Ax preserves lengths.
C. If a set S={u1,...,up} has the property that ui⋅uj=0 whenever
i≠j, then S is an orthonormal set.
D. Not every orthogonal set in Rn is a linearly independent
set.
E. An orthogonal matrix is invertible.
Problem 7 | Discrete logarithms with respect to different
primitive roots
Prove that the difficulty of the discrete logarithm problem is
independent of the primitive root.
Specifically, for any prime p, assuming that it is computationally
feasible to extract discrete
logarithms with respect to one primitive root of p, show how one
can feasibly extract discrete
logarithms with respect to any other primitive root of p.