[mg85923] Re: How to select terms wanted in a series

[Fabian <NOSPAM_fahasch at yahoo.de>]

On Wed, 27 Feb 2008 09:46:27 +0000 (UTC), Barrow <GRseminar 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!

try Coefficient[expression, Times[x,y]]

Cheers,
  Fabian