Re: Log manipulation
- To: mathgroup at smc.vnet.net
- Subject: [mg16845] Re: Log manipulation
- From: Jens-Peer Kuska <v-jkuska>
- Date: Thu, 1 Apr 1999 21:35:21 -0500
- Organization: Wolfram Research, Inc.
- References: <7dprc6$dq3@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Pierre,
no. The transformation Log[a_]+Log[b_] :> Log[a*b]
is only valid for real a and b . If you know that
a and b are real and will be never complex you can setup
the transformation by hand with
LogSimplify[expr_]:=expr //. {a_.*Log[b_]+c_.*Log[d_] :> Log[b^a*d^c],
Log[Exp[a_]:> a}
Hope that helps
Jens
Pierre infelta wrote:
>
> I am sure this is a classic but I don't seem to find the answer.
>
> I am looking for the command that will do the opposite of powerExpand
> for the Log function.
>
> If I have
>
> PowerExpand[Log[a*b]]
> I get
>
> Log[a] +Log[b]
>
> Is there a command that does the opposite?
>
> Command[Log[a] + Log[b]]
>
> to get
>
> Log[a b]
>
> as an answer
>
> Thanks