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Re: Finding an exponent?

  • To: mathgroup at
  • Subject: [mg112375] Re: Finding an exponent?
  • From: David Bailey <dave at>
  • Date: Sat, 11 Sep 2010 05:45:16 -0400 (EDT)
  • References: <i6crg4$sak$>

On 10/09/10 09:50, AES wrote:
> Given  Exp[ expr ]  where   expr  is some complex expression in Standard
> form, how can I get  expr  itself in an Input cell?   (Preferably
> unevaluated, and other than using manual Copy and Paste).
> Log[Exp[expr]] doesn't seem to do it.

1. Presumably you realise that Log is a multivalued function (you can 
always add one or more multiples of 2 Pi I to the answer).

2. Since this expression was presumably the result of an evaluation, it 
shouldn't evaluate any further if you strip the Exp off it.

To ignore the multivalued nature of Log, just use PowerExpand.

Alternatively, you could decide that you are doing a structural, rather 
than mathematical operation (as you would be if you used copy/paste) and use

Part[Exp[expr], 2]

David Bailey

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