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Re: How to select terms wanted in a series

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85960] Re: How to select terms wanted in a series
  • From: Grischika at mail.ru
  • Date: Thu, 28 Feb 2008 03:00:58 -0500 (EST)
  • References: <fq3bhj$gas$1@smc.vnet.net>

On 27 =C6=C5=D7, 11:46, Barrow <GRsemi... at gmail.com> wrote:
> Dear all,
>
> I have an expression, which is a sum of large number of terms, e.g.
>
> expression = x + 2x*y - x*y*z + u*x*y + 3u^2
>
> And I want to select out terms with the factor (x*y). e.g.
>
> The terms in "expression" that I want are 2x*y, -x*y*z, u*x*y
>
> My first step is,
>
> allterms = Apply[List, expression]
>
> Then, I don't know how to extract the terms I want, I use
>
> Select[allterms, (# == x*y*_)&]
>
> But It doesn't work.
>
> Anyone has some good ideas? any help will be appreciated much!
> Sincerely =9ABarrow

There are many ways to do this. I prefer the next one:
Apply[List,Expand[Coefficient[e1, x*y]*x*y]].


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