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MathGroup Archive 2000

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LogPlot != Plot[Log]

  • To: mathgroup at
  • Subject: [mg24266] LogPlot != Plot[Log]
  • From: "Gy. Csanady" <csanady at>
  • Date: Wed, 5 Jul 2000 23:10:47 -0400 (EDT)
  • Organization: gsf
  • References: <>
  • Sender: owner-wri-mathgroup at

Dear Steve Christensen,

I should like to post the following question to the Mathgroup. I am
relatively new with Mathematica and I encountered a problem..

Dear MathGroup,
I should like to demonstrate some transformation rules graphically using
Mathematica extended capabilities. However, the simplest example failed:
Let assume a simple exponential function with real parameters:

C1[t_] := C0*Exp[-kel*t]

param = {C0 -> 100, kel -> 1}

we can plot the function easily:

g1 = Plot[C1[t] /. param, {t, 0, 2}, PlotRange -> {{0, 2}, {10, 100}}]

We can also make a half- logarithmic plot:

g2 = Plot[Log[E, C1[t]] /. param, {t, 0, 2}, PlotStyle -> {RGBColor[0, 0, 1],
Dashing[{0.05, 0.05}]},  PlotRange -> {{0, 2}, {Log[10], Log[100]}}]

In addition we can convert the y-axis to a logarithmic one:

g3 = Show[g2, Ticks -> Join[{FullOptions[g2, Ticks][[1]], FullOptions[g2,
Ticks][[2]] /. {x_, y_Real, len_, style_} :> {x, Exp[y], len, style}}]]

We can obtain a half-logarithmic plot by using the LogPlot function:

<< Graphics`Graphics`

g4 = LogPlot[C1[t] /. param, {t, 0, 2}, PlotRange -> {{0, 2}, {10, 100}}]

Now I would expect that plot g4 and g3 become identic:

Show[{g3, g4}, PlotRange -> All]

But it is not the case. I am sure that there is something wrong. Any help
would be appreciated.
With best regards
Gy. Csanady

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