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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: [mg35232] RE: [mg35214] Simplifying the *Individual Coefficients* in Series Expansions?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Wed, 3 Jul 2002 05:13:46 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Try using the third form of Collect with h = Simplify.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 

> From: AES [mailto:siegman at stanford.edu]
To: mathgroup at smc.vnet.net
> 
> 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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