3. Let n = 4 (we choose 4 for calculation simplicity, but the following are true for arbitrary n). Let S: R →R be a linear transformation such that S(In) = n, and S(AB) = S(BA) for all n x n matrices A, B. In this problem, we will show that S and tr (defined in problem 2) are the same linear transformation. %3D (A) Let i e {1, 2, .. ,n}. Let eii € Rn² be the matrix with 1 on the (i, i)-entry, and 0 everywhere else. Calculate that S(eu) = 1. Hint. Let j e {1, 2, -.. , n} with i # j. Calculate S(eijeji) and S(ejieij) respectively. (B) Let i, j e {1,2, -. ,n} with i # j. Let eij e R" be the matrix with 1 on the (i, j)-entry, and 0 everywhere else. Calculate that S(es) = 0. Hint. Calculate S(eijejj) and S(ejjeij) respectively. (C) Let A be anxn matrix such that tr(A) = 0. Use (1) and (2) to conclude S(A) = 0. %3D (D) Use problem 1 to conclude S(X)= tr(X), for all n x n matrix X.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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please solve number 3
3.
Let n = 4 (we choose 4 for calculation simplicity, but the following
are true for arbitrary n). Let S: R" →R be a linear transformation such that S(In) = n, and
S(AB) = S(BA) for all n x n matrices A, B. In this problem, we will show that S and tr (defined
in problem 2) are the same linear transformation.
(A) Let i e {1, 2, - . , n}. Let ei € R"² be the matrix with 1 on the (i, i)-entry, and 0
everywhere else. Calculate that S(e) = 1.
Hint. Let j€ {1, 2, -.. ,n} with i # j. Calculate S(eij@ji) and S(ej;eij) respectively.
Let i, j e {1,2, ·. ,n} with i # j. Let eij e R" be the matrix with 1 on the
(B)
(i, j)-entry, and 0 everywhere else. Calculate that S(eis) = 0.
Hint. Calculate S(eijejj) and S(ejjeij) respectively.
(C) Let A be anxn matrix such that tr(A) = 0. Use (1) and (2) to conclude S(A)
= 0.
(D) Use problem 1 to conclude S(X)
tr(X), for all n x n matrix X.
1
Transcribed Image Text:3. Let n = 4 (we choose 4 for calculation simplicity, but the following are true for arbitrary n). Let S: R" →R be a linear transformation such that S(In) = n, and S(AB) = S(BA) for all n x n matrices A, B. In this problem, we will show that S and tr (defined in problem 2) are the same linear transformation. (A) Let i e {1, 2, - . , n}. Let ei € R"² be the matrix with 1 on the (i, i)-entry, and 0 everywhere else. Calculate that S(e) = 1. Hint. Let j€ {1, 2, -.. ,n} with i # j. Calculate S(eij@ji) and S(ej;eij) respectively. Let i, j e {1,2, ·. ,n} with i # j. Let eij e R" be the matrix with 1 on the (B) (i, j)-entry, and 0 everywhere else. Calculate that S(eis) = 0. Hint. Calculate S(eijejj) and S(ejjeij) respectively. (C) Let A be anxn matrix such that tr(A) = 0. Use (1) and (2) to conclude S(A) = 0. (D) Use problem 1 to conclude S(X) tr(X), for all n x n matrix X. 1
1.
„ Let S, T : R"m → R be linear transformations. Suppose that ker S C ker T.
Show that there exists a fixed scalar a E R such that T(x) = aS(x) for all x E R™.
Hint. Use rank-nullity theorem.
2.
trace.
Let n = 4 (we choose 4 for calculation simplicity, but the following are true for arbitrary n).
Consider the following linear transformation:
tr : Rn?
a11
a12
a13
ain
a21
а22
a23
A2n
n
a31
a32
a33
a3n
Haji + a22+ a33 + · · · + ann =
i=1
anl an2 an3
Ann
(1) .
that tr(In) = n.
Let In be the n x n identity matrix (or equivalently, a vector in Rn). Calculate
(2)
tr(AB) =
Let A, B be two n x n matrices (or equivalently, a vector in Rn). Calculate that
tr(BA).
Hint. Write A = [aij] and B = [bki]. Write down the diagonal of AB and BA in terms of aij
and bki. Then cотрute tr(AB) and tr(BA).
Transcribed Image Text:1. „ Let S, T : R"m → R be linear transformations. Suppose that ker S C ker T. Show that there exists a fixed scalar a E R such that T(x) = aS(x) for all x E R™. Hint. Use rank-nullity theorem. 2. trace. Let n = 4 (we choose 4 for calculation simplicity, but the following are true for arbitrary n). Consider the following linear transformation: tr : Rn? a11 a12 a13 ain a21 а22 a23 A2n n a31 a32 a33 a3n Haji + a22+ a33 + · · · + ann = i=1 anl an2 an3 Ann (1) . that tr(In) = n. Let In be the n x n identity matrix (or equivalently, a vector in Rn). Calculate (2) tr(AB) = Let A, B be two n x n matrices (or equivalently, a vector in Rn). Calculate that tr(BA). Hint. Write A = [aij] and B = [bki]. Write down the diagonal of AB and BA in terms of aij and bki. Then cотрute tr(AB) and tr(BA).
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