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MathGroup Archive 2004

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Re: "+ -" in an output line?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52298] Re: [mg52275] "+ -" in an output line?
  • From: yehuda ben-shimol <benshimo at bgu.ac.il>
  • Date: Sun, 21 Nov 2004 07:23:40 -0500 (EST)
  • References: <200411200841.DAA08791@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Out[13] is not kept as a standard "Mathematical expression". It is kept 
within a header of  a SeriesData as you can see below. The - comes from 
the Complex[0,-1] and the + comes (probably) from some sort of 
displaying this object as a mathematical expression on the screen but 
not evaluated..
Running the following commands
a = Series[-I q s - I p Sqrt[K12 - s2], {s, 0, 1}];
FullForm[a]


SeriesData[s, 0, List[Times[Complex[0, -1],
    p, Power[Plus[K12, Times[-1, s2]], Rational[1,
      2]]], Times[Complex[0, -1], q]], 0, 2, 1]

will show you that.
But if you run
b = Normal[a];
FullForm[b]

Plus[Times[Complex[0, -1], q, s], Times[Complex[0, -1], p,
    Power[Plus[K12, Times[-1, s2]], Rational[1, 2]]]]

you can notice that this is an evaluated regular expression of Mathematica

Anyway, I think that this should not appear and hope it will be corrected
yehdua

AES/newspost wrote:

>The input
>
>    In[13]:=
>    Series[-I q s - I p Sqrt[K1^2 - s^2], {s, 0, 1}]
>
>gives
>
>    Out[13]=
>    -I Sqrt[K1^2] p + - I q s + O[s^2]
>
>whereas
>
>    In[14]:=
>    Series[-I q s - I p Sqrt[K1^2 - s^2], {s, 0, 1}] // Normal
>
>gives
>
>    Out[14]=
>    -I Sqrt[K1^2] p - I q s
>
>What's that "+ -" doing in Out[13] ?  Is this normal?
>
>  
>


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