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Mathematica LogPlot Bug

  • To: mathgroup at smc.vnet.net
  • Subject: [mg123707] Mathematica LogPlot Bug
  • From: AntonioP <ant.piniz at gmail.com>
  • Date: Fri, 16 Dec 2011 05:47:08 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

Hello,

I have to draw some functions in log scale, but LogPlot seems not to
be able to draw them correctly if the y-value is too small.
A simple case:

f[x_] = 10^(-5 x)
LogPlot[f[x], {x, 1, 100}, PlotRange -> Full]

the plot should be a simple straight line for any x value,
while at about x=61.5 there is a step and, for any greater value of x,
the function appears to be constant.
Nevertheless, Mathematica is able to compute the correct value of f[x]
for any x:

N[f[60]]
N[f[65]]
N[f[80]]
N[f[100]]

There is a similar problem for large y-values, as well.
Apparently there is a y-range, about (10^-308, 10^308), outside which
LogPlot doesn't work correctly.

Any idea on how to resolve the problem?


Thanks,

Antonio



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