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MathGroup Archive 2004

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Re: extracting powers and coefficients from a polynomial

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49134] Re: extracting powers and coefficients from a polynomial
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Fri, 2 Jul 2004 02:01:44 -0400 (EDT)
  • Organization: The University of Western Australia
  • References: <cbrcau$iqc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <cbrcau$iqc$1 at smc.vnet.net>,
 "AngleWyrm" <no_spam_anglewyrm at hotmail.com> wrote:

> I have made a formula that produces a polynomial expansion, and I wish to
> extract the powers and coefficients into a list.
> 
> Expand[(Sum[x^i, {i, 6}])^3]
>   1x^3 + 3x^4 + 6x^5 + 10x^6 + 15x^7 + 21x^8 + 25x^9 + 27x^10 + 27x^11 + 
>   25x^12
> + 21x^13 + 15x^14 + 10x^15 + 6x^16 + 3x^17 + 1x^18
> 
> How do I make a table of the powers and coefficents?
> 3, 1
> 4, 3
> 5, 6
> 6, 10
> ....

Pattern-matching is an easy way of doing this:

  poly = Expand[(Sum[x^i, {i, 6}])^3]

  List @@ poly /. c_. x^n_. -> {n, c}

Cheers,
Paul

-- 
Paul Abbott                                   Phone: +61 8 9380 2734
School of Physics, M013                         Fax: +61 8 9380 1014
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AUSTRALIA                            http://physics.uwa.edu.au/~paul


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