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@Patrice et all : Maybe it would be interesting to combine both methods? As in this example.<br>
Nothing is perfect!<br>
It is certainly necessary to code a routine directly to postscript. (Herbert ?) <br>
<br>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br>
\documentclass{article}<br>
\usepackage{pstricks,pst-func}<br>
\SpecialCoor<br>
\def\FieldLines{%<br>
/r1 xP xA sub dup mul yP dup mul add sqrt def<br>
/r2 xP xA add dup mul yP dup mul add sqrt def<br>
/V q1 r1 div<br>
q2 r2 div<br>
add def<br>
% Ex=-dV/dx<br>
/Ex q1 xP xA sub mul r1 3 exp div<br>
q2 xP xA add mul r2 3 exp div<br>
add def<br>
% Ey=-dV/dy<br>
/Ey yP<br>
q1 r1 3 exp div<br>
q2 r2 3 exp div<br>
add mul def<br>
/NormeE Ex dup mul Ey dup mul add sqrt def<br>
/dX Ex NormeE div pasX mul def<br>
/dY Ey NormeE div pasX mul def<br>
}<br>
\begin{document}<br>
\begin{center}<br>
\begin{pspicture*}(-6,-6)(6,6)<br>
% les limites<br>
\pstVerb{/xmin -5 def /xmax 5 def /ymin -5 def /ymax 5 def}%<br>
% le pas d'itération<br>
\pstVerb{/pasX 0.025 def}%<br>
\pstVerb{/q1 1 def % les charges<br>
/q2 1 q1 mul def<br>
/xA -2.2 def}%<br>
% 15 degrés entre chaque ligne (24*15=360)<br>
\multido{\iA=0+24}{15}{% 15 lignes de champ<br>
\pstVerb{/xStart xA def<br>
/pasX q1 q1 abs div 0.05 mul def<br>
/xP xStart pasX \iA\space cos mul add def<br>
/yP 0 pasX \iA\space sin mul add def}%<br>
\parametricplot[plotpoints=2000,linecolor=blue]{xmin}{xmax}{%<br>
\FieldLines<br>
/xP xP dX add def<br>
/yP yP dY add def<br>
xP yP<br>
}<br>
\pstVerb{/xStart xA neg def<br>
/pasX q2 q2 abs div 0.05 mul def<br>
/xP xStart pasX \iA\space cos mul add def<br>
/yP 0 pasX \iA\space sin mul add def}%<br>
\parametricplot[plotpoints=2000,linecolor=blue]{xmin}{xmax}{%<br>
\FieldLines<br>
/xP xP dX add def<br>
/yP yP dY add def<br>
xP yP<br>
}}<br>
\def\Potentiel{/r1 x xA sub dup mul y dup mul add sqrt def<br>
/r2 x xA add dup mul y dup mul add sqrt def<br>
/V q1 r1 div<br>
q2 r2 div<br>
add def<br>
V<br>
}<br>
\pstVerb{/y 0 def<br>
/Valeurs [<br>
-6 1 0 {/x exch def \Potentiel } for<br>
] def<br>
}%<br>
\multido{\i=0+1}{7}{%<br>
\psplotImp[linestyle=dotted,linecolor=red](-5,-5)(5,5){%<br>
\Potentiel Valeurs \i\space get sub}}%<br>
\pscircle[fillstyle=solid](!xA 0){0.2}\pscircle[fillstyle=solid](!xA neg 0){0.2}<br>
\end{pspicture*}<br>
\end{center}<br>
\end{document}<br>
<br>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br>
<br>
</font></font>Best regards,</span><span style="font-size: 10pt;" lang="EN-US"><br>
<br>
</span><span style="font-size: 10pt;">Manuel</span></div>
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