[pstricks] using the xylogscale of pst-plot vs gnuplot exponent issue

[Julien Morand]

Hello everyone,

I'm currently trying to plot the curve of the theoretical RdSOn of a power
 MOSFET like in the example:

http://commons.wikimedia.org/wiki/File:Bv_rdson.png

I try to use the psgraph environment of pst-plot but when I write the given
equation the plot is not correct. I have to modify the value of the
exponent from 2.5 to 320!!

I also try the same equation using gnuplot and the plot is correct (see
attached files). Is there anyone that could help me on with this issue?
here is my code:

\documentclass[pstricks]{standalone}

%

\usepackage[T1]{fontenc}

\usepackage{xunicode}

\usepackage[francais]{babel}

\usepackage{multicol}

%%%%%%%%%%%%%%%%%%%%%%%%%

%ps tricks package

\usepackage{pstricks}

\usepackage{pstricks-add}

\begin{document}

%PSPICTURE

\begin{pspicture}(-1.3,-0.5)(10.3,7.1)

%%%%%%%%%%%%%%%%%%%%%%%%%%

%putting the option for the psgraph environment

\psset{xAxisLabel=$V_{br}(V)$,yAxisLabel=$\displaystyle
R_{sp\acute{e}cifique}\left(\frac{\Omega}{cm^2} \right)$,urx=-9cm,ury=0.5cm}

%%%%%%%%%%%%%%%%%%%%%%%%%%

%starting the psgraph envrionement with automatic scale

\begin{psgraph}

[tickcolor=lightgray,subtickcolor=lightgray,subticksize=0.5,Ox=1,Dx=1,xsubticks=9,xylogBase=10,logLines=all,Oy=-4,Dy=1,ysubticks=9]
{->}(1,-4)(1,-4)(3.301,1.18){11cm}{6cm}

%%%%%%%%%%%%%%%%%%%%%%%%%%

%plotting the theoretical rdson without leads resistance

\psplot[linecolor=darkgray,linestyle=dashed]{1.69879}{3.301}{0.00000000593
320 x exp mul log}

\end{psgraph}

%

\end{pspicture}

%

\end{document}


thanks
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