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Undesired horizontal line in Plot / Bug?

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  Undesired horizontal line in Plot / Bug? "H Hogreve" <hogreve@ifisr.org> - 2011-04-14 08:58 +0000
    Re: Undesired horizontal line in Plot / Bug? Albert Retey <awnl@gmx-topmail.de> - 2011-04-14 11:08 +0000
      Re: Undesired horizontal line in Plot / Bug? "Kevin J. McCann" <Kevin.McCann@umbc.edu> - 2011-04-15 07:54 +0000

#1673 — Undesired horizontal line in Plot / Bug?

A phenomenon that occasionally also occurs in other plots
can be exemplified by setting

fD[n_, cZ_] := 137^2/Sqrt[1 + cZ^2/(137*n + Sqrt[137^2 - cZ^2])^2];

and plotting, e.g., 

Plot[{fD[1, z], fD[5, z]}, {z, 1, 137}, Frame -> True, 
 PlotRange -> Automatic]

There is a horizonal line visible (parallel to the abscissa)
that should not be there!! In fact, other plots like, e.g.,

Plot[{fD[1, z], fD[2, z]}, {z, 1, 137}, Frame -> True, 
 PlotRange -> Automatic]

look fine, without this annoying additional line. Unfortunately,
I could not find a way to remove or suppress this unwanted
horizontal line in the first plot. Moreover, I observed this 
effect in all versions of Mathematica I have access to at the
moment, i.e., four, six, and seven, and it makes me wonder
whether this is a yet unresolved bug.

Thus I would be very grateful for any hints on the questions

  - whether this horizontal line also occurs in the
    current Mathematica 8.0 ?
  - is there any remedy to prevent the line from being
    plotted or to remove it from the plot?

Many thanks in advance for your kind help, H. Hogreve

P.S.: If plotted without Frame, then this line does not
 occur, but apparently at its position the new abscissa
 is placed

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#1678

Hi,

> A phenomenon that occasionally also occurs in other plots
> can be exemplified by setting
>
> fD[n_, cZ_] := 137^2/Sqrt[1 + cZ^2/(137*n + Sqrt[137^2 - cZ^2])^2];
>
> and plotting, e.g.,
>
> Plot[{fD[1, z], fD[5, z]}, {z, 1, 137}, Frame ->  True,
>   PlotRange ->  Automatic]
>
> There is a horizonal line visible (parallel to the abscissa)
> that should not be there!! In fact, other plots like, e.g.,
>
> Plot[{fD[1, z], fD[2, z]}, {z, 1, 137}, Frame ->  True,
>   PlotRange ->  Automatic]
>
> look fine, without this annoying additional line. Unfortunately,
> I could not find a way to remove or suppress this unwanted
> horizontal line in the first plot. Moreover, I observed this
> effect in all versions of Mathematica I have access to at the
> moment, i.e., four, six, and seven, and it makes me wonder
> whether this is a yet unresolved bug.

> Thus I would be very grateful for any hints on the questions
>
>    - whether this horizontal line also occurs in the
>      current Mathematica 8.0 ?

it does not appear there..

>    - is there any remedy to prevent the line from being
>      plotted or to remove it from the plot?
>
> P.S.: If plotted without Frame, then this line does not
>   occur, but apparently at its position the new abscissa
>   is placed

you were almost there: if you say Frame->True, that does not 
automatically mean Axes->False, so depending on some heuristics a axes 
might be drawn or not. That is what you see in older versions, but even 
there you can avoid the axes explicitly:

Plot[{fD[1, z], fD[5, z]}, {z, 1, 137}, Frame -> True,
  PlotRange -> Automatic,
  Axes -> False]

hth,

albert

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#1699

I don't see it with Windows7 64-bit Mathematica 8.0.1

fD[n_, cZ_] := 137^2/Sqrt[1 + cZ^2/(137 n + Sqrt[137^2 - cZ^2])^2];
Plot[{fD[1, z], fD[5, z]}, {z, 1, 137}, Frame -> True,
  PlotRange -> Automatic]

Kevin

On 4/14/2011 7:08 AM, Albert Retey wrote:
> fD[n_, cZ_] := 137^2/Sqrt[1 + cZ^2/(137*n + Sqrt[137^2 - cZ^2])^2];
>>
>>  and plotting, e.g.,
>>
>>  Plot[{fD[1, z], fD[5, z]}, {z, 1, 137}, Frame ->   True,
>>     PlotRange ->   Automatic]

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