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MathGroup Archive 2007

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Re: Extracting terms of a multivariate polynomial order by order

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80295] Re: Extracting terms of a multivariate polynomial order by order
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 16 Aug 2007 07:26:02 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <fa13t2$p5c$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

CoefficientArrays[Expand[(1 + x + y + z)^3], {x, y, z}] /.
  s_SparseArray :> Normal[s]

may help you.

Regards
   Jens

Marcus P S wrote:
> Hello,
> 
>   I have a multivariate polynomial (3 variables) from which I would
> like to extract terms order by order.  More explicitly, I want all the
> lowest order terms, or all terms of the form
> 
> c(L,M,N) x^L y^M z^N
> 
>   where L+M+N is smallest, and c(LMN) is some coefficient.  If I have
> this, I can extract order by order, and taylor to which order I want
> to approximate my polynomial.
> 
>   I considered "Coefficients", but if I ask for the coefficients of
> the form x^2 z^2, it may return something like "1 + y", which is not
> what I want.  Moreover, I have to explicitly request each possible
> term of a given order, which seems too mechanical/repetitive to be the
> "right way"  to do things.  The function for manipulating SeriesData
> objects are similarly limited.
> 
>   I am assuming that there is function in Mathematica (even 5.2) that
> will do this.  Any suggestions would be greatly welcome.
> 
>   Thanks in advance.
> 
>   Marcus Silva
> 
> 


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