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MathGroup Archive 2005

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Re: Transformation rule problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58044] Re: Transformation rule problem
  • From: Roland Franzius <roland.franzius at uos.de>
  • Date: Fri, 17 Jun 2005 05:18:41 -0400 (EDT)
  • Organization: Universitaet Hannover
  • References: <d8rnfg$l4b$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Oliver Buerschaper schrieb:
> Hi there,
> 
> I'm stuck with a problem concerning transformation rules and was 
> wondering whether somebody could give me a hint on this. I wouldn't 
> mind a complete solution either ;-) Here's the problem:
> 
> In a sum like for example
> 
> a^2 b^4 + a^3 b + a^5 + a^5 b
> 
> I'd like to replace every instance of the product (a b) by a different 
> expression, let's call it d. Thus my result should look like
> 
> d^2 b^2 + a^2 d + a^5 + a^4 d
> 
> This replacement is required to work for arbitrary a and b (especially 
> when they're functions). I've already tried some simple transformation 
> rules but they couldn't do the job.

a^2 b^4 + a^3 b + a^5 + a^5 b/.
{Power[a, m___ : 1] *Power[b, n___ : 1] :>
Power[d, Min[m,n]]*Power[a, m - Min[m, n]] *Power[b, n - Min[m, n]]}

is working for your example

-- 

Roland Franzius

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