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MathGroup Archive 2006

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Re: efficient term collection algorithm

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69179] Re: efficient term collection algorithm
  • From: "sashap" <pavlyk at gmail.com>
  • Date: Fri, 1 Sep 2006 06:40:37 -0400 (EDT)
  • References: <ed68a7$jci$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Try using Collect:

In[1]:= e=a/i+b/j+c/i;

In[2]:= Collect[e, i^(-1)]

        a + c   b
Out[2]= ----- + -
          i     j

Oleksandr Pavlyk
Wolfram Research

Blake Laing wrote:
> Dear Math Group
>
> I wish to combine terms in a expression which share a denominator, such
> as in the following simple case:
>
> In[1]:=
> a/i+b/j+c/i//.Plus[Times[A_.,Power[denom_,-1]],Times[B_.,Power[denom_,-1]]]:>
>       Factor[Plus[A,B]Power[denom,-1]]//InputForm
> Out[1]//InputForm=
> (a + c)/i + b/j
>
> The actual expression I am working with contains thousands of terms, and
> a pairwise algorithm such as this is wholly inadequate. Will one of you
> please suggest a more efficient way to combine each additive term in a
> large expression with a shared denominator?
>
> Thanks,
> 
> Blake Laing
> physics grad student
> University of Oklahoma


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