RFC: extracting coefficients of a multivariate polynomial
Subject: RFC: extracting coefficients of a multivariate polynomial
From: Stavros Macrakis
Date: Thu, 24 Apr 2008 13:45:58 -0400
For operations on polynomials, it is best to represent your
expressions in Canonical Rational Expression (CRE) form, which you do
using the rat(...) operation. After that, ratcoeff(expr, var, degree)
is efficient, especially if the variable is the main variable of the
expression. To choose the main variable, either use ratvars or
rat(..., var3, var2, var1), where var1 is the principal variable, e.g.
ex: rat((x+y+z)^3, z,y,x) =>
x^3+(3*y+3*z)*x^2+(3*y^2+6*z*y+3*z^2)*x+y^3+3*z*y^2+3*z^2*y+z^3
ratcoef(ex,x,1) => 3*z^2+6*y*z+3*y^2
rat((x+y+z)^3, x,y,z) =>
z^3+(3*y+3*x)*z^2+(3*y^2+6*x*y+3*x^2)*z+y^3+3*x*y^2+3*x^2*y+x^3
Try it out and let us know....
-s
On Thu, Apr 24, 2008 at 1:28 PM, andre maute <andre.maute at gmx.de> wrote:
> I have to extract the coefficients of a multivariate polynomial.
> The monomials appearing in the multivariate polynomial are given.