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MathGroup Archive 1995

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Re: Dealing with Indeterminant points & ListPlot

  • To: mathgroup at
  • Subject: [mg2076] Re: Dealing with Indeterminant points & ListPlot
  • From: David Harvatin <dtharvat at>
  • Date: Sat, 23 Sep 1995 20:36:38 -0400
  • Organization: University of Colorado at Boulder

Ed Oswalt <efo at> wrote:
>I am using the latest Student version of Mathematica and was having a 
>problem dealing with indeterminant points in in a function like
>Sin[x]/x where Sin is indeterminant at x = 0 (but by L'Hopitals is
>equal to 1. When I try to plot such functions Mathematica complains.
>What can I do to get around this? Can I use an If[] function inside
>other functions like Plot[] to test for x = 0 and sub in the value
>1 for the formula in that instance? How do I do that - tried and
>can't get it to work right.
>I just started with Mathematica this weekend and was a little
>dissapointed since my HP-48GX calculator handles these functions fine
>(not sure if attempts L'Hopital's or just follows the convergance to
>1).  I plan to e-mail them the suggestion to handle these points better
>(even if it means a switch to activativate finding a symbolic
>L'Hopitals solution or just following where the convergance appears to
>be at.
>Also I am using ListPlot[] on the same student windows version and the dots
>are too small - they are invisable on the screen and barely visable on 
>print out, I end up having to join the points so I can see them but that is 
>not what I want to show - I want to show the points. Any Idea's on how to
>make these dots "Fatter"?
>Thanks for any help,
>Ed Oswalt 
>Part time student & Full Time Engineer
>efo at


In response to your first question regarding the sinc function : For plotting and other 
numerical purposes use sinc[x_] = If[x != 0, Sin[x]/x, 1].  If you try to integrate this new 
function, MMA objects to the discontinuity at x = 0.  In this case, I would recommend a set of 
signal processing packages written by Brian Evans, where he has defined a sinc function that 
MMA can deal with in integration.  I don't know how he did it, but you can check his code.  He 
uses the name "Sinc".  The packages are freely available on MathSource (FTP :, and the PC version of the file is called "".  Be sure 
to follow his installation instructions to the letter.

In response to your second question, make sure that the "Make Lines Thin" option under the 
Graph menu does not have a check mark by it, and make sure that "Show Lines" does have a check 
mark by it.  Then enlarge the graphic by dragging with the mouse.  I have found this to help in 
some cases with the ListPlot command.  A better solution might be to use the SetOptions, 
PlotStyle, and PointSize commands.  Good luck.

Dave Harvatin
dtharvat at

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