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MathGroup Archive 2000

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Re: LogPlot != Plot[Log]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24299] Re: LogPlot != Plot[Log]
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 7 Jul 2000 00:11:40 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <200006020649.CAA05402@smc.vnet.net> <8k0ugn$q5l@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

hmm - the plots are identical. But LogPlot[] uses not the
natural base it uses base 10. 

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

gives the same curve as LogPlot[].
The reason is very simple. Every semi-log paper has a base 10 scale
and *not* a E scale. If anyone make a LogPlot[] he wish to have
the same result as on semi-log paper.

Regards
  Jens

> 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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