MACM 401/MATH 701/MATH 801 Assignment 2, Spring 2023
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MACM 401/MATH 701/MATH 801
Assignment 2, Spring 2023.
Due Monday February 6th at 11pm. For problems involving Maple calculations and Maple programming, you should export your work to a .pdf file. Late Penalty: -20% for up to 24 hours late. Zero after that.
Question 1 (15 marks): The Extended Euclidean Algorithm
Given a, b e E, a Euclidean domain, the extended Euclidean algorithm solves sa + tb = g for s, t e E and g = gcd(a, b). More generally, for k = 0, 1, ..., n, n+1 it computes (rk , sk , tk ) e E3 where r0 = a, r1 = b, rn+1 = 0 and sk a + tk b = rk for 0 < k < n + 1.
(a) For integers a = 99, b = 28 execute the extended Euclidean algorithm by hand. Use the tabular method presented in class that shows the values for rk , sk , tk , qk . Identify b − 1 mod a.
(b) Program the extended Euclidean algorithm for Q[x] in Maple. The input is two non-
zero polynomials a, b e Q[x]. The output is three polynomials (s, t, g) where g is the monic gcd of a and b and sa + tb = g holds.
Please print out the values of (rk , sk , tk ) that are computed after each division step so that we can observe the exponential growth in the size of the rational coefficients of the rk , sk , tk polynomials.
Use the Maple commands quo(a,b,x) and/or rem(a,b,x) to compute the quotient and remainder of a divided b in Q[x]. Remember, in Maple, you must explicitly expand
products of polynomials using the expand( . . .) command.
Execute your Maple code on the following inputs.
> a := expand((x+1)*(2*x^4-3*x^3+5*x^2+3*x-1));
> b := expand((x+1)*(7*x^4+5*x^3-12*x^2-x+4));
Check that your output satisfies sa + tb = g and check that your result agrees with Maple’s g := gcdex(a,b,x,’s’,’t’); command.
(c) Consider a(x) = x3 - 1, b(x) = x2 + 1, and c(x) = x2 . Apply the algorithm in the proof of Theorem 2.6 (as presented in class) to solve the polynomial diophantine equation σa + τ b = c for σ, τ e Q[x] satisfying deg σ < deg b - deg g where g is the monic gcd of a and b. Use Maple’s g := gcdex(a,b,x,’s’,’t’); command to solve sa + tb = g for s, t e Q[x] or use your code from part (b).
Question 2 (15 marks): Multivariate Polynomials
(a) Consider the polynomial
A = 3 + 4y5 + 7x3 z + 5x2y2 z2 + 9x2y3 + 6xy2 z .
Write A in graded lexicographical order with x > y > z .
Write A in pure lexicographical order with x > y > z .
Write A in pure lexicographical order with y > x > z .
For each case write down lc(A), lm(A) and lt(A).
See the MultiPolyDefinitions handout for lecture 6.
(b) Consider the polynomials
A = 6 y2 x3 + 2 x2y2 + 5 yx2 + 3 xy2 + yx + y2 + x + y and B = 2 yx2 + x + y .
You are to divide the polynomials A by B over z. Write A e z[y][x] and test if B|A by doing the division in z[y][x] by hand. If B|A determine the quotient Q of A ÷ B .
Note, the quotient must be a polynomial in z[y][x]. Show your working. Repeat the calculation using
A = 6 y2 x3 + 2 x2y2 + 6 yx2 + 3 xy2 + yx + y2 + x + y Check your answers using Maple’s divide command.
Question 3 (15 marks): The Primitive Euclidean Algorithm
Reference section 2.7
(a) Calculate the content and primitive part of the following polynomial a e z[x, y], first as a polynomial in z[y][x] and then as a polynomial in z[x][y], i.e., first with x the main variable then with y the main variable. Use the Maple command gcd to calculate
the GCD of the coefficients. The coeff command will be useful. > a := expand( (x^4-3*x^3*y-x^2-y)*(8*x-4*y+12)*(2*y^2-2) );
(b) By hand, calculate the pseudo-remainder and the pseudo-quotient q˜ of the polyno- mials a(x) divided by b(x) below where a, b e z[y][x].
> a := 3*x^3+(y+1)*x;
> b := (2*y)*x^2+2*x+y;
Now compute and q˜ using Maple’s prem command to check your work.
(c) Given the following polynomials a, b e z[x, y], calculate the GCD(a, b) using the prim- itive Euclidean algorithm with x the main variable.
> a := expand( (x^4-3*x^3*y-x^2-y)*(2*x-y+3)*(8*y^2-8) );
> b := expand( (x^3*y^2+x^3+x^2+3*x+y)*(2*x-y+3)*(12*y^3-12) ); You may use the Maple commands prem, gcd and divide for intermediate calculations.
Question 4 (20 marks): Chinese Remaindering
Reference section 5.3.
(a) By hand, find 0 < u < M where M = 5 x 7 x 9 such that
u = 3 mod 5, u = 1 mod 7, and u = 3 mod 9
using the “mixed radix representation” for u.
(b) We will solve the Chinese remainder problem in F [y].
Theorem: Let F be a field and let m1 , m2 , . . . , mn and u1 , u2 , . . . , un be polynomi- als in F [y] with deg(mi ) > 0 for 1 < i < n. If gcd(mi , mj ) = 1 for 1 < i < j < n then there exists a unique polynomial u in F [y] s.t.
(i) u = ui (mod mi ) for 1 < i < n and
(ii) u = 0 or deg u < deg mi .
Prove the theorem by modifying the proof of the Chinese remainder theorem for z to work for F [y]. Note, the congruence relation u = ui (mod mi ) means mi |(u - ui ) in F [y].
A = x4 + x3 + x + 1 and B = x3 + 1
in the ring zp [x] for p = 2. Use Maple to compute AB, gcd(A, B), the remainder of
A ÷ B, and to solve SA + TB = G in zp [x] for S, T, G where G = gcd(A, B). See the handout PolynomialOperations.pdf from lecture 6 for the Maple commands.
Now solve the following Chinese remainder problem in F [y] for F = z2 . Find u e z2 [y] such that
u = y2 (mod y3 + y + 1) and u = y2 + y + 1 (mod y3 + y2 + 1).
2023-02-03