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MathGroup Archive 2004

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Re: What does +- mean?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47563] Re: [mg47519] What does +- mean?
  • From: Oleksandr Pavlyk <pavlyk at phys.psu.edu>
  • Date: Fri, 16 Apr 2004 05:20:29 -0400 (EDT)
  • Organization: Penn State University; Department of Physics
  • References: <200404150739.DAA11584@smc.vnet.net>
  • Reply-to: pavlyk at phys.psu.edu
  • Sender: owner-wri-mathgroup at wolfram.com

Hi, This seems to be the bug. This is seen looking
at FullForm of your series

In[1]:=
FullForm[Series[
    Sqrt[-2^(-1) + x^2],
    {x, 0, 4}]]

Out[1]//FullForm=
FullForm[SeriesData[x, 0,
    {Complex[0, 1]*1/Sqrt[2],
     0,
     (Complex[0, -1])*1/Sqrt[2],
     0,
     (Complex[0, Rational[-1, 2]])*1/Sqrt[2]},
     0, 5, 1]]

This is what we should expect, and hence we have the display bug.
It seems to be only present is coefficient of expansion involve
radicals. The following modification of your example displays OK.

Series[ -1/4 + x^2, {x, 0, 4} ]

Regards,
Oleksandr Pavlyk

Lautaro Vergara wrote:

> Hi,
> 
> I have found (v. 5.0) an extrange thing: when one expands, e.g.,
> 
> Series[Sqrt[-1/2+x^2],{x,0,4}]
> 
> there appear a +- sign (which is correctly not present when one changes
> -1/2 by -1)
> 
> is this a bug or a feature?
> 
> Thanks
> 
> L. Vergara


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