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MathGroup Archive 1999

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RE: Re: Simplify Log[ab] - Log[b] to Log[a] ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16098] RE: [mg16071] Re: [mg16039] Simplify Log[ab] - Log[b] to Log[a] ?
  • From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
  • Date: Thu, 25 Feb 1999 08:24:57 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

David Reiss wrote:

...... this might not be what the user wants (if z<0 for example).
However,


In[3]:=
(z^2)^(1/2) (Log[a b]-Log[b])/.{Log[x_ y_]:>Log[x]+Log[y]}

Out[3]= Sqrt[z^2]*Log[a]

It all depends on the broader context of the problem.

____________________

Remember you can also use FunctionExpand, PowerExpand, ComplexExpand with
pattern matching.  This saves you the trouble of typing in obscure
identities, and will not neglect the branch cut for Sqrt[expr].


In[1]:=
Gamma[3,x]*Sqrt[z^2]/.
  Gamma[args__]:>FunctionExpand[Gamma[args]]

Out[1]=
(x^2/E^x + 2*(E^(-x) + x/E^x))*
  Sqrt[z^2]



Regards,
Ted Ersek


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