       Re: Expansion Coefficients in Multivariate Series Expansions?

• To: mathgroup at smc.vnet.net
• Subject: [mg26603] Re: [mg26579] Expansion Coefficients in Multivariate Series Expansions?
• From: Tomas Garza <tgarza01 at prodigy.net.mx>
• Date: Thu, 11 Jan 2001 10:39:13 -0500 (EST)
• References: <200101090651.BAA00200@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```I don't see why Coefficient[] doesn't work?

In:=
d = (a*x + b*y + c*z)^5
Out=
(a*x + b*y + c*z)^5
In:=
Coefficient[d, x^2*y^2*z]
Out=
30*a^2*b^2*c
In:=
Coefficient[d, x*y*z^3]
Out=
20*a*b*c^3
In:=
Coefficient[d, x*y^3*z]
Out=
20*a*b^3*c

Unless, of course, I didn't quite get your question.

Tomas Garza
Mexico City
----- Original Message -----
From: "A. E. Siegman" <siegman at stanford.edu>
To: mathgroup at smc.vnet.net
Subject: [mg26603] [mg26579] Expansion Coefficients in Multivariate Series Expansions?

> Given an expression that is the sum of products of integer powers of
> three variables (say x,y,z) multiplied by numerical coefficients:
>
>    f = c000 + c100 x + c010 y + c001 z + c110 x y + c211 x^2 y z + . . .
>
> where the  cijk's are all real numbers, and f may or may not be in
> Normal (or other) form, how do I find the coefficient of a particular
> term, e.g. c100 for the x term (*not*  c1000 + c110 y), or  ckmn for the
> x^k y^m z^n term?
>
> Neither Coefficient nor SeriesCoefficient seems to do this -- and the
> SeriesCoefficient[expr, {n1,n2,n3,..}] syntax seems to be mentioned but
> neither explained or illustrated in the on-line Help.
>
> Thanks, siegman at stanford.edu
>

```

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