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PowerExpand

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63537] PowerExpand
  • From: "Blimbaum, Jerry CIV NSWC PC" <jerry.blimbaum at navy.mil>
  • Date: Wed, 4 Jan 2006 03:17:14 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com
  • Thread-index: AcYQsFUAKHiJwoSiQf6H6XDPKu9E6Q==

Just want to make a comment.....Normally PowerExpand is looked upon as a
culprit because for the general case it leads to wrong
results......However, I had an interesting case where I tried

Siimplify[expr, m>0]  ....expr was of 2 basic  forms (although really
more complicated then this, but this shows the basic idea)

   .....Sqrt[-m^2 (a^2+b^2)]  and   Sqrt[m^2 (a^2+b^2)] 

With Simplify Mathematica cranked and cranked and cranked  with no
output.....So , in  frustration,  I tried PowerExpand and a second later
it performed the same operation with surprising ease and the result was
exactly what i was trying to get...

If I try the basic expressions  , then Simplify took m out of the Square
Root sign  for the Sqrt[m^2 (a^2+b^2)]   but  not  for Sqrt[-m^2
(a^2+b^2)] 


jerry blimbaum



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