ASKSAGE: Sage Q&A Forum - Latest question feedhttp://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Mon, 27 Mar 2017 14:26:48 -0500Division algorithm in a polynomial ring with variable coefficientshttp://ask.sagemath.org/question/37098/division-algorithm-in-a-polynomial-ring-with-variable-coefficients/ I am working on an algorithm to divide a polynomial `f` by a list of polynomials `[g1, g2, ..., gm]`. The following is my algorithm:
def div(f,g): # Division algorithm on Page 11 of Using AG by Cox;
# f is the dividend;
# g is a list of ordered divisors;
# The output consists of a list of coefficients for g and the remainder;
# p is the intermediate dividend;
n = len(g)
p, r, q = f, 0, [0 for x in range(0,n)]
while p != 0:
i, divisionoccured = 0, False
print(p,r,q);
while i < n and divisionoccured == False:
if g[i].lt().divides(p.lt()):
q[i] = q[i] + p.lt()//g[i].lt()
p = p - (p.lt()//g[i].lt())*g[i]
divisionoccured = True
else:
i = i + 1
if divisionoccured == False:
r = r + p.lt()
p = p - p.lt()
return q, r
Here is an example of implementing the algorithm:
K.<a,b> = FractionField(PolynomialRing(QQ,'a, b'))
P.<x,y,z> = PolynomialRing(K,order='lex')
f=a*x^2*y^3+x*y+2*b
g1=a^2*x+2
g2=x*y-b
div(f,[g1,g2])
Here is the result:
(a*x^2*y^3 + x*y + 2*b, 0, [0, 0])
(((-2)/a)*x*y^3 + x*y + 2*b, 0, [1/a*x*y^3, 0])
(x*y + 4/a^3*y^3 + 2*b, 0, [1/a*x*y^3 + ((-2)/a^3)*y^3, 0])
(4/a^3*y^3 + ((-2)/a^2)*y + 2*b, 0, [1/a*x*y^3 + ((-2)/a^3)*y^3 + 1/a^2*y, 0])
(((-2)/a^2)*y + 2*b, 4/a^3*y^3, [1/a*x*y^3 + ((-2)/a^3)*y^3 + 1/a^2*y, 0])
(2*b, 4/a^3*y^3 + ((-2)/a^2)*y, [1/a*x*y^3 + ((-2)/a^3)*y^3 + 1/a^2*y, 0])
Error in lines 6-6
Traceback (most recent call last):
and some other error messages.
We can see that it worked well until the leading term is `2b`. it does not recognize the `2b` as a term. I tried:
(x).lt().divides(1)
It gives the answer `False`. But I tried
(x).lt().divides(a)
It gives error message. Is there a way to solve this? Thank you for your help!
KittyLMon, 27 Mar 2017 14:26:48 -0500http://ask.sagemath.org/question/37098/