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MathGroup Archive 1999

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Re: Not Plotting Vertical Assymptotes

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18594] Re: [mg18542] Not Plotting Vertical Assymptotes
  • From: BobHanlon at aol.com
  • Date: Tue, 13 Jul 1999 01:01:27 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Patrick,

The solution is just to generate separate plots for each region.

f[x_] := 1/(1 - x);
pole = x /. Solve[1/f[x] == 0, x][[1]];
plt1 = Plot[f[x], {x, 0, pole}, DisplayFunction -> Identity];
plt2 = Plot[f[x], {x, pole, 2}, DisplayFunction -> Identity];
Show[{plt1, plt2}, DisplayFunction -> $DisplayFunction];

g[x_] := 1/((.75 - x)(1 - x)(1.25 - x));
pole = x /. Solve[1/g[x] == 0, x];
rng = Prepend[ #, x] & /@ Partition[Append[Prepend[pole, 0], 2], 2, 1];
Show[Plot[g[x], #, DisplayFunction -> Identity, PlotRange -> {-750, 750}] & 
/@ 
      rng, DisplayFunction -> $DisplayFunction];

Bob Hanlon

In a message dated 7/10/99 8:12:14 AM, p_mclean at postoffice.utas.edu.au writes:

>Anyone have any idea how to stop Plot putting a (near) vertical line at
>x=2 in the command:
>
>      Plot[1/(1-x),{x,0,2}]
>
>ie. detect that the function 1/(1-x) has a singularity at x=2 and do
>something about it. This is analagous to numerically integrating over a
>(integrable) singularity, where the following remedy works:
>
>      NIntegrate[1/Abs[Sqrt[x-1]]^2,{x,0,1,2}]
>
>But in this case it doesn't work. Decreasing MaxBend works a bit but the
>line is still there.
>
>(I am really interested in drawing paths in the plane using ParmetricPlot)
>
>Any ideas or comments
>


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