Re: coefficient of a polynomial term
- To: mathgroup at smc.vnet.net
- Subject: [mg59360] Re: [mg59339] coefficient of a polynomial term
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Sun, 7 Aug 2005 03:46:55 -0400 (EDT)
- References: <200508060529.BAA01135@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On 6 Aug 2005, at 07:29, Tun Myint Aung wrote:
> Dear Mathgroup,
>
> One more question again! How to extract the coefficient of a
> polynomial term. For example:
>
> poly = 2 x^2 +3 x*y +4 y^2+x^3
>
> I would like to get 2 for first term, 3 for second term, 4 for
> third term and so on..
>
> Thank everyone for answering my questions
>
>
> With Regards,
>
> Tun Myint Aung
>
>
0ne way is to use the built in function CoefficientList:
poly = 2 x^2 +3 x*y +4 y^2+x^3;
ls = CoefficientList[poly, {x, y}]
{{0, 0, 4}, {0, 3, 0}, {2, 0, 0}, {1, 0, 0}}
This returns an array, where the coefficient of x^i y^j is the entry
ls[[i+1,j+1]], for example the coefficient of y^2 is
ls[[1,3]]
4
There are also undocumented algebra functions whose output contains
the coefficients of a polynomial, for example
s=Internal`DistributedTermsList[poly,{x,y}]
{{{{3, 0}, 1}, {{2, 0}, 2}, {{1, 1}, 3}, {{0, 2}, 4}},
{x, y}}
You can extract the coefficients with, for example:
s[[1,All,1]][[All,1]]
{3,2,1,0}
Andrzej Kozlowski
- References:
- coefficient of a polynomial term
- From: "Tun Myint Aung" <tma@nus.edu.sg>
- coefficient of a polynomial term