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MathGroup Archive 1993

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Re: plotting graphs with asymptotes

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Re: plotting graphs with asymptotes
  • From: Jack K. Cohen <jkc at dix.mines.colorado.edu>
  • Date: Sun, 5 Sep 93 06:34:41 -0600

Tom Wickham-Jones at Wolfram, solved this problem elegantly a few months ago
in response to a similar query.  I made a nice NeXT notebook---mail me
if you can take NeXTMail.  But here is Tom's code:

Unprotect[Plot];
Plot[ f_, {x_, lims__ /; Length[ {lims}] > 2}, opts___] :=
Module[ (* Tom Wickham-Jones, WRI *)
        {temp, eps = 10^-15, d},
       
        temp =
        Partition[{lims}, 2, 1]; (* make pairs offset by 1 *)
  
        temp =
        ( d = (#[[2]] - #[[1]])*eps; (* get a delta *)
          # + {d, -d}  (* shrink both ends by delta *)
        )&  (* map over pairs to get shrunken pairs *)
        /@ temp;

        temp =
        Plot[f, Evaluate[Prepend[#,x]], (* iter triplets *)
                    DisplayFunction -> Identity, opts
        ]& /@ temp;

        Show[temp, DisplayFunction -> $DisplayFunction]]       
Protect[Plot];

---
I call this "elegant" because you use this extended Plot in an already
existing Mma syntax (that of NIntegrate) by specifying extra internal
points at singularities:

Plot[Tan[x], {x, 0, Pi/2, 3Pi/2, 2Pi}]





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