Re: Dealing with Indeterminant points & ListPlot

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

Ed Oswalt <efo at pixel.kodak.com> 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 dtc.kodak.com > > > > Ed, 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 : mathsource.wri.com), and the PC version of the file is called "SigProc2_IBM_PC.zip". 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 sprint.uccs.edu