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Re: How to select terms wanted in a series

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85926] Re: [mg85916] How to select terms wanted in a series
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Thu, 28 Feb 2008 02:43:21 -0500 (EST)
  • References: <200802270933.EAA16377@smc.vnet.net>

On Feb 27, 2008, at 4:33 AM, Barrow 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.
>

I would use Coefficient:

List@@Coefficient[expression,x y] x y

Regards,

Ssezi


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