Multivariate polynomial manipulation

[songuke]

Hi all,

I'm almost new to sympy and are very excited about the polynomial
module in sympy. Basically I want to retrieve the coefficient matrix
and the monomial vector of a system of polynomials. I tried
Poly.all_coeffs and Poly.monoms but the functions threw the exception:
PolynomialError: multivariate polynomials not supported

May I know how good the support of multivariate polynomial is in
sympy? If I want to extend the polynomial module to implement these
features, could anybody show me where to start? What is the difficulty
in implementing these functions for multivariate polynomials?

Regards,
Son.

[Aaron Meurer]

We have fairly full support of multivariate polynomials. all_coeffs
apparently doesn't work for univariate polynomials. I think what you
want instead is just coeffs:

In [33]: Poly(3*x*y + 2*x**2 + 3*y*x**2).coeffs()
Out[33]: [3, 2, 3]

This uses lex order by default, but you can use any ordering.

monoms works for me:

In [29]: Poly(3*x*y + 2*x**2 + 3*y*x**2).monoms()
Out[29]: [(2, 1), (2, 0), (1, 1)]

You can easily combine these to get the coefficients by term. We
don't have specific functions to get a coefficient matrix, but it
should be pretty straight forward to get using these functions.

Aaron Meurer

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