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MathGroup Archive 2005

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Re: question about HoldForm

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60808] Re: question about HoldForm
  • From: Peter Pein <petsie at dordos.net>
  • Date: Thu, 29 Sep 2005 05:41:22 -0400 (EDT)
  • References: <dhdbc3$8eg$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Ruth Lazkoz schrieb:
> Hi,
> 
> I have this expression
> 
> x = 2; HoldForm[x^2 + 4x + 4]
> 
> Is there a way to operate on HoldForm so that I get (x^2+2)^2? If I cut 
> a paste the result and operate on it I obviously get 16.
> 
> Thanks,
> 
> Ruth
> 
> 
In[1]:=
x=2;hf=HoldForm[x^2+4x+4];

the obvious:

In[2]:= hf/.HoldForm[x^2+4x+4]->HoldForm[(x^2+2)^2]
Out[2]= (x^2+2)^2

this unfotunately changes the structure (HoldForm "slides down" to x^2):
In[3]:= Factor@ReleaseHold[hf/.HoldPattern[x]->HoldForm[x^2]]
Out[3]= (2+x^2)^2

In[4]:= %//FullForm
Out[4]//FullForm= Power[Plus[2,HoldForm[Power[x,2]]],2]

... but why do you want this unusual mapping (x^2+4x+4 -> (x^2+2)^2)?
;-)

Peter


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