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MathGroup Archive 1999

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Re: Not Plotting Vertical Assymptotes

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18616] Re: [mg18542] Not Plotting Vertical Assymptotes
  • From: "Wolf, Hartmut" <hwolf at debis.com>
  • Date: Tue, 13 Jul 1999 01:01:36 -0400
  • Organization: debis Systemhaus
  • References: <199907100618.CAA02940@smc.vnet.net.>
  • Sender: owner-wri-mathgroup at wolfram.com

Hello Patrick

Patrick McLean schrieb:
> 
> 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.
> 
Perhaps there is a better method, but a quick fix would be:

In[3]:=
g1=Plot[1/(1-x),{x,0,1},DisplayFunction->Identity]

In[4]:=
g2=Plot[1/(1-x),{x,1,2},DisplayFunction->Identity]

In[5]:=
Show[g1,g2,PlotRange->{{0,2},Automatic},DisplayFunction->$DisplayFunction]

maybe that helps a little bit (Of course you could forge the idea to a
real program) ....

....ok, e.g. like that:

In[31]:= Unprotect[Plot]

In[32]:=  Plot[f_,{var_Symbol,min_,sing__,max_},opts___]:=
	Module[{ranges=Prepend[#,var]&/@Partition[{min,sing,max},2,1], g},
		g=Map[Plot[f,#,opts,DisplayFunction->Identity]&,ranges];
                Show[g,DisplayFunction->$DisplayFunction]]

In[33]:= Protect[Plot]

In[34]:= Plot[1/((1-x)(2-x)),{x,0,1,2,3},PlotRange->{All,{-50,50}}]

---your's hw



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