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Re: Replace not spotting a replacement

  • To: mathgroup at smc.vnet.net
  • Subject: [mg103433] Re: [mg103399] Replace not spotting a replacement
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 21 Sep 2009 05:52:57 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

Make the LHS of a rule as simple as possible

sub = Solve[Equal @@ (Sqrt[2*Pi*\[Tau]] -> \[Mu]), \[Tau]][[1]]

{\[Tau] -> \[Mu]^2/(2*Pi)}

Simplify[Sqrt[2*Pi]*\[Tau]^(3/2) /. sub, 
 Element[\[Mu], Reals]]

Abs[\[Mu]]^3/(2*Pi)

Simplify[Sqrt[2*Pi]*\[Tau]^(3/2) /. sub, 
 \[Mu] >= 0]

\[Mu]^3/(2*Pi)


Bob Hanlon

---- claranet news <david at carter-hitchin.clara.co.uk> wrote: 

=============
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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