Re: Simplifying the *Individual Coefficients* in Series Expansions?
- To: mathgroup at smc.vnet.net
- Subject: [mg35219] Re: Simplifying the *Individual Coefficients* in Series Expansions?
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Wed, 3 Jul 2002 05:13:15 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <afrh3q$lu4$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
Collect[fS,x,Simplify]
??
Because
"Collect[expr, x] collects together terms involving the same powers of \
objects matching x. Collect[expr, {x1, x2, ... }] collects together
terms \
that involve the same powers of objects matching x1, x2, ... .
Collect[expr, var, h] applies h to the expression that forms the
----------------------------------------------------------------
coefficient of each term obtained"
---------------------------------
Regards
Jens
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?