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MathGroup Archive 2002

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Re: Simplifying the *Individual Coefficients* in Series Expansions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35235] Re: [mg35214] Simplifying the *Individual Coefficients* in Series Expansions?
  • From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
  • Date: Wed, 3 Jul 2002 05:14:22 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

What do you mean by: "will not evaluate numerically"???
I was going to suggest simply:

Collect[Simplify[fS],x]

but this ought to produce something similar to your last approach, and 
since I can't see anything wrong with that I can't tell if the same 
problem will not occur with my proposed solution.

Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/


On Tuesday, July 2, 2002, at 03:12  PM, AES wrote:

> I have a long expression  f   that involves integers times various
> powers of symbols  b  and  x, i.e.
>
>     f = ratio of two lengthy polynomials in  b  and  x
>
> If I series expand this in  x , viz.
>
>     fS  = Series[f,  {x, 0, 2}] // Normal
>
> I get an answer in the form
>
>     fS =  c1 x + c2 x^2
>
> where the coefficients  c1  and  c2   in the resulting series expansion
> come out as rather messy expressions (ratios of polynomials).  In my
> problem, however, these coefficients actually happen to simplify
> substantially (since there are common factors in their numerators and
> denominators), and I'd like to have them in simplified form.  But if I
> write
>
>     fS // Simplify
>
> I'm back in lengthy polynomial form; and if I try something like
>
>     fS = (Coefficient[fS, x] // Simplify) x +
>                                 (Coefficient[fS, x^2] // Simplify) x^2
>
> I get an expression that looks great, but will not evaluate numerically.
>
> Any easy way around this?
>
>
>



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