Re: How to get coefficient list from a Series Command
- To: mathgroup at smc.vnet.net
- Subject: [mg114446] Re: How to get coefficient list from a Series Command
- From: Ray Koopman <koopman at sfu.ca>
- Date: Sat, 4 Dec 2010 06:16:23 -0500 (EST)
- References: <idakdb$m2u$1@smc.vnet.net>
On Dec 3, 3:30 am, Autt <kajornrungsil... at gmail.com> wrote:
> Greeting,
> I've a list issued from multivariate series like : K={a1+a2*x +a3*y
> +a4*x^2*+a5*x*y +a6*y^2 }
> I need to have {a1, a2 , a3 ,a4,a5,a6}
>
> How to do that please?
> e.g.
> n = 3
> u = Normal[Series[x^4 + y^4 + x^2, {x, 5, n}, {y, 5, n}]]
> c[0] = {};
> d = {};
> q[0] = {};
> For[k = 1 , k <= n - 1, k++,
> For[i = 0 , i <= k , i++,
> p[i, k - i] =
> SeriesCoefficient[u, {x, 5, i}, {y, 5, k - i}];
> q[k] = Union[{q[k - 1], {p[i, k - i]}}];
> d = Union[d, q[k]];
>
> Print[d];
>
> Best regard,
c = CoefficientList[u,{x,y}]
{{-1250,500,-150,20},{500,0,0,0},{-149,0,0,0},{20,0,0,0}}
c[[i,j]] is the coefficient of x^(i-1)*y^(j-1).
TableForm[c, TableHeadings->MapThread[#1^Range[0,#2-1]&,
{{x,y},Dimensions@c}], TableAlignments->Right]
1 y y^2 y^3
1 -1250 500 -150 20
x 500 0 0 0
x^2 -149 0 0 0
x^3 20 0 0 0