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Re: Replace not spotting a replacement

  • To: mathgroup at smc.vnet.net
  • Subject: [mg103430] Re: [mg103399] Replace not spotting a replacement
  • From: "David Park" <djmpark at comcast.net>
  • Date: Mon, 21 Sep 2009 05:52:24 -0400 (EDT)
  • References: <22608339.1253442945257.JavaMail.root@n11>

Replace does not Solve or do algebra. Replace only matches a pattern and
that pattern does not occur in your expression.

Solve for Tau in terms of Mu and then replace.

Sqrt[2 \[Pi] \[Tau]] == \[Mu]
\[Tau]sol = Part[Solve[%, \[Tau]], 1, 1]
Sqrt[2 \[Pi]] \[Tau]^(3/2) /. \[Tau]sol


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: claranet news [mailto:david at carter-hitchin.clara.co.uk] 


Hi Folks,

Seems the replace function is being a bit dim here.  This fails:

Sqrt[2 \[Pi]] \[Tau]^(3/2) /. Sqrt[ 2 \[Pi] \[Tau]] -> \[Mu]

Apologies if this is an FAQ - I couldn't see anything about it.  What do I 
need to do here to coerce Mathematica into making this replacement? I tried
using the 
Collect function on tau first, but that didn't seem to work.  I also tried 
re-writing the replacement rule as

Sqrt[2 \[Pi]] \[Tau]^(3/2) /. Sqrt[ 2 \[Pi] ] t^(1/2) -> \[Mu]

But still no joy.

Anyone know?

Many thanks,
David.





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