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MathGroup Archive 1995

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Mathematica conundrum

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1782] Mathematica conundrum
  • From: Zorro <berriz at husc.harvard.edu>
  • Date: Sun, 30 Jul 1995 21:35:46 -0400
  • Organization: Harvard University, Cambridge, Massachusetts

Hi.  When I issue the command

  Plot[Exp[-5x],{x, 0, 5}, PlotRange->{0,1}];

Mathematica produces the plot without a hitch.  Similarly, when I
issue

  Plot[Exp[-x],{x, 0, 5}];

Likewise, the command

  Plot[Evaluate[Table[Sin[n x],{n, 5}]],
       {x, 0, 1}, PlotRange->{-1, 1}];

produces, as expected, a series of superimposed sine waves.  BUT,
Mathematica balks at

  Plot[Evaluate[Table[Exp[-nx],{n, 5}]],
       {x, 0, 5}, PlotRange->{0, 1}];

spitting out

  Plot::plnr: 
     CompiledFunction[{x}, <<1>>, -C<<11>>-][x]
       is not a machine-size real number at x = 0..
  Plot::plnr: 
     CompiledFunction[{x}, <<1>>, -C<<11>>-][x]
       is not a machine-size real number at x = 0.208333.
  Plot::plnr: 
     CompiledFunction[{x}, <<1>>, -C<<11>>-][x]
       is not a machine-size real number at x = 0.416667.
  General::stop: 
     Further output of Plot::plnr
       will be suppressed during this calculation.

... and an empty plot (two axes, no graphs).

Why is this?  What could the error messages mean??  After all,
Exp[-nx] is well-behaved everywhere, and reasonably valued in the
requested ranges of x and n.  ( I have no problems when I try to
produce the plots individually (for each value of n), nor when I use
Show to combine them in a single plot...)

And the meta-follow up: is there a reference I could have looked up
(besides possibly reading Wolfram's book cover-to-cover) to find the
answer to this question?

Thanks for your help.

Z.


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