RFC: extracting coefficients of a multivariate polynomial
Subject: RFC: extracting coefficients of a multivariate polynomial
From: Richard Fateman
Date: Thu, 24 Apr 2008 10:45:55 -0700
try something like this
zz:rat((1+x+y)^5);
for i:0 thru 5 do (h:ratcoef(zz,x,i),for j:0 thru 5 do
c[i,j]:ratcoef(h,y,j));
If you have only polynomials, doing poly:rat(poly) once should do it all.
> -----Original Message-----
> From: maxima-bounces at math.utexas.edu
> [mailto:maxima-bounces at math.utexas.edu] On Behalf Of andre maute
> Sent: Thursday, April 24, 2008 10:29 AM
> To: maxima at math.utexas.edu
> Subject: RFC: extracting coefficients of a
> multivariate polynomial
>
> Hi all,
>
> I have to extract the coefficients of a multivariate polynomial.
> The monomials appearing in the multivariate polynomial are given.
>
> For now I'm using the following function,
> which is also the bottleneck of my application.
>
> ---------------------------------------------------------------
> display2d : false;
>
> v : [x,y];
> exps : [[0,2], [0,0], [1,1], [0,1], [1,0], [2,0]];
> poly : a00 + a10*x + a01*y + a20*x^2 + a11*x*y + a02*y^2;
>
> my_coeff(v,exps,poly) := block(
>
> [c,k,l,h],
>
> c : [],
> for k : 1 thru length(exps) do block(
> h : poly,
> for l : 1 thru length(v) do block(
> if exps[k][l] # 0 then block(
> h : coeff(h,v[l],exps[k][l])
> )
> ),
> for l : 1 thru length(v) do block(
> h : subst(0,v[l],h)
> ),
> h : ratsimp(h),
> c : append(c,[h])
> ),
>
> return(c)
>
> )$
>
> my_coeff(v,exps,poly);
> ---------------------------------------------------------------------
>
> Does someone know,
> if Maxima does have such a function, a potentially faster one?
>
> The documentation of Maxima revealed nothing for me :-(
>
> Kind Regards,
> Andre
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