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MathGroup Archive 2001

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RE: PowerExpand in mathematica

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31871] RE: [mg31843] PowerExpand in mathematica
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 8 Dec 2001 05:51:48 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Peter,

I think that the correct answer is 1/t, not -1/t. Nevertheless, this is just
the type of problem that PowerExpand might give the incorrect answer.
PowerExpand is an operation that in general is done at your own risk.

Try a series expansion on the parts of your expression. Or plot your
expression and 1/t. Or try this

Series[(-1/t)^(3/2) Sqrt[-t], {t, 0, 10}]
1/t + O[t]^4

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/



> From: Peter [mailto:ptrsn2001 at yahoo.com]
To: mathgroup at smc.vnet.net
>
> Hi,
>
> Is this a known bug, feature? Or I am doing something wrong?
> -------------------------------
> Mathematica 4.0 for Linux
> Copyright 1988-1999 Wolfram Research, Inc.
>  -- Motif graphics initialized --
>
> In[1]:= PowerExpand[(-1/t)^(3/2) Sqrt[-t]]
>
>         1
> Out[1]= -
>         t
> ---------------------------------
> The correct answer is -1/t, of course.
>
> Thanks,
> Peter
>



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