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Re: [Please Help] How to get coefficient list from a

  • To: mathgroup at smc.vnet.net
  • Subject: [mg114428] Re: [Please Help] How to get coefficient list from a
  • From: =?tis-620?b?zdTKw+zD0aqq7CCiqMPD2OinyA==?= at smc.vnet.net
  • Date: Sat, 4 Dec 2010 06:13:05 -0500 (EST)

Thank you for your answer. But I would like only the coefficient of series
equation in the form {a1, a2 , a3 ,a4,a5,a6} not to be in the form of {{a1,
a3, a6}, {a2, a5, 0}, {a4, 0, 0}}. How to get there?
Best regard


2010/12/3 Bob Hanlon <hanlonr at cox.net>

>
> expr1 = a1 + a2*x + a3*y + a4*x^2 + a5*x*y + a6*y^2;
>
> coef = CoefficientList[expr, {x, y}]
>
> {{a1, a3, a6}, {a2, a5, 0}, {a4, 0, 0}}
>
> From example in documentation on CoefficientList
>
> expr2 = Fold[FromDigits[Reverse[#1], #2] &, coef, {x, y}]
>
> a1 + a2 x + a4 x^2 + (a3 + a5 x) y + a6 y^2
>
> expr1 == expr2 // Simplify
>
> True
>
>
> Bob Hanlon
>
> ---- Autt <kajornrungsilp.i 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,
>
>
>
>
> --
>
> Bob Hanlon
>
>


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