MATH 5112 ALGEBRA 2 HOMEWORK 4
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HOMEWORK 4
MATH 5112 ALGEBRA 2
(1) Suppose that q is a prime power, and Fq is the field with q elements. (a) How many linear maps are there from Fq(m) to Fq(n)?
(b) If m n, how many injective linear maps are there from Fq(m) to Fq(n)?
(c) If m ≥ n, how many surjective linear maps are there from Fq(m) to Fq(n)?
(d) If r min{m,n}, how many linear maps are there from Fq(m) to Fq(n) that have rank r?
(2) Suppose that F is a field, V and W are F-vector spaces of dimension m and n respectively. (a) Show that there is a unique F-linear map
Φ : S2(V ⌦ W) ! S2(V) ⌦ S2(W) ⊕ V2 (V) ⌦V2 (W)
with the property that
Φ (v1 ⌦ w1 )(v2 ⌦ w2 ) = ((v1v2 ) ⌦ (w1w2 ), (v1 ^ v2 ) ⌦ (w1 ^ w2 )). (b) If the characteristic of F is not 2, show that Φ is a linear isomorphism.
(3) Suppose F is a field and V,W are F-vector spaces. If f 2 V? = HomF(V,F) and g 2 W? then there exists a unique F-linear map φ(f,g) : V ⌦ W ! F with the property φ(f,g)(v ⌦ w) = f(v)g(w) for all v 2 V and w 2 W .
(a) Show that there is a unique F-linear map
Φ : V? ⌦ W? ! (V ⌦ W)?
with the property Φ(f ⌦ g) = φ(f,g) for all f 2 V? , g 2 W? .
(b) Show that Φ is injective.
(c) Give an example, where V and W are infinite dimensional and Φ is not surjective.
(4) For each of the Z- modules below, give the Invariant Factor Form, and the Elementary divisor form.
(a) Z/(8) ⊕ Z/(9) ⊕ Z/(10) ⊕ Z/(12);
(b) The cokernel of the Z-module homomorphism φ : Z3 ! Z3 given by
φ 0 1b(a) 0 1 0 1b(a)
c 4 9 16 c
(5) The characteristic polynomial of a complex 5 ⇥ 5 matrix A is (x − 1)3 (x + 1)2 . What are the possible rational canonical forms of A? For each of these cases, also give the Jordan canonical form and the minimum polynomial of A.
(6) Let V be the 5-dimensional vector space of complex polynomials in z of degree 4. Define φ : V ! V by φ(p(z)) = p00 (z)+ x2p(0), where p00 (z) is the second derivative of p(z). (a) Give the matrix A of φ with respect to the basis {1,z,z ,z ,z }234 of V .
(b) What is the rational canonical form of A?
(c) What is the Jordan canonical form of A?
2022-04-19