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The dierence between these sorts is best shown by an

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Unformatted text preview: l contains only one unknown, x, then the terms might contain x3 , x1 = x, and x0 = 1 as in the case of the polynomial x3 − 2x + 1. If more than one unknown exists, then a term may also contain a product of the unknowns, as in the polynomial x3 + 3x2 y + y 2 . Coeﬃcients can be integers (as in the previous examples), rational numbers, irrational numbers, ﬂoating-point numbers, complex numbers, or other variables. > x^2 - 1; x2 − 1 > x + y + z; x+y+z > 1/2*x^2 - sqrt(3)*x - 1/3; 1 12 √ x − 3x − 2 3 > (1 - I)*x + 3 + 4*I; (1 − I ) x + 3 + 4 I 60 • Chapter 3: Finding Solutions > a*x^4 + b*x^3 + c*x^2 + d*x + f; a x4 + b x3 + c x2 + d x + f Maple possesses commands for many kinds of manipulations and mathematical calculations with polynomials. The following sections investigate some of them. Sorting and Collecting The sort command arranges a polynomial into descending order of powers of the unknowns. Rather than making another copy of the polynomial with the terms in order, sort modiﬁes the way Maple stores the original polynomial in memory. In other words, if you display your polynomial after sorting it, it retains the new order. > sort_poly := x + x^2 - x^3 + 1 - x^4; sort _poly := x + x2 − x3 + 1 − x4 > sort(sort_poly); −x4 − x3 + x2 + x + 1 > sort_poly; −x4 − x3 + x2 + x + 1 Maple sorts multivariate polynomials in two ways. The default method sorts them by total degree of the terms. Thus, x2 y 2 will come before both x3 and y 3 . • The other option sorts by pure lexicographic order (plex), ﬁrst by the powers of the ﬁrst variable in the variable list (second argument) and then by the powers of the second variable in the variable list. The diﬀerence between these sorts is best shown by an example. > mul_var_poly := y^3 + x^2*y^2 + x^3; mul _var _poly := y 3 + x2 y 2 + x3 3.4 Polynomials > sort(mul_var_poly, [x,y]); • 61 x2 y 2 + x3 + y 3 > sort(mul_var_poly, [x,y], ’plex’); x3 + x2 y 2 + y 3 The collect command groups coeﬃcients of like powers in a polynomial. For example, if the terms ax and bx are in a polynomial, Maple collects them as (a + b)x. > big_poly:=x*y + z*x*y + y*x^2 - z*y*x^2 + x + z*x; big _poly := x y + z x y + y x2 − z y x2 + x + z x > collect(big_poly, x); (y − z y ) x2 + (y + z y + 1 + z ) x > collect(big_poly, z); (x y − y x2 + x) z + x y + y x2 + x Mathematical Operations You can perform many mathematical operations on polynomials. Among the most fundamental is division, that is, to divide one polynomial into another and determine the quotient and remainder. Maple provides the commands rem and quo to ﬁnd the remainder and quotient of a polynomial division. > r := rem(x^3+x+1, x^2+x+1, x); r := 2 + x > q := quo(x^3+x+1, x^2+x+1, x); q := x − 1 62 • Chapter 3: Finding Solutions > collect( (x^2+x+1) * q + r, x ); x3 + x + 1 Sometimes it is suﬃcient to know whether one polynomial divides into another polynomial exactly. The divide command tests for exact polynomial division. > divide(x^3 - y^3, x - y); true > rem(x^3 - y^3, x - y, x); 0 You evaluate polynomials at values as you would with any expression, by using eval. > poly := x^2 + 3*x - 4; poly := x2 + 3 x − 4 > eval(poly, x=2); 6 > mul_var_poly := y^2*x - 2*y + x^2*y + 1; mul _var _poly := y 2 x − 2 y + y x2 + 1 > eval(mul_var_poly, {y=1,x=-1}); −1 Coeﬃcients and Degrees The commands degree and coeff determine the degree of...
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This note was uploaded on 08/27/2012 for the course MATH 1100 taught by Professor Nil during the Spring '12 term at National University of Singapore.

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