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