在以下情况下如何使用 linestyle=dashed？

Question

\documentclass[12pt,pstricks,border=10pt]{standalone}
\usepackage{pst-electricfield}
\begin{document}
\psset{unit=1.25cm}
\begin{pspicture}(-5,-3)(4,3.5)
\def\figure{\begin{pspicture*}(-4.5,-3)(4.5,3)
\psframe*[linecolor=green!20](-4.5,-3)(4.5,3)
\psLineSegments[arrowsize=.15cm]{->}(-2,0)(-1,0)(-2,0)(-2.75,0)(2,0)(1,0)(2,0)(2.75,0)
\psgrid[subgriddiv=0,gridcolor=lightgray,griddots=10]
\psElectricfield[Q={[1 -2 0][1 2 0]},N=21,Pas=0.0155]
\foreach \n in {6,7,8,9,11.5,20}{
\psEquipotential[Q={[1 -2 0][1 2 0]},Vmin=\n,Vmax=\n](-5,-5)(5,5)}
\psline(0,-2.5)(0,2.5)
\psline(0,0.2)(.2,.2)(.2,0)
\psLineSegments[arrowsize=1.5mm]{->}(0,0)(0,0.75)(0,0)(0,1.5)(0,0)(0,-0.75)(0,0)(0,-1.5)
\psset{linestyle=none,fillstyle=solid}
\pscircle[fillcolor=white](-2.05,0){2mm}
\pscircle[fillcolor=white](2,0){2mm}
\pscircle*(-2,0){1.1mm}
\pscircle*(2,0){1.1mm}
\uput{.6pt}[135](-2,0){\tiny \pscirclebox*[framesep=0pt]{$+Q$}}
\uput{.6pt}[45](2,0){\tiny \pscirclebox*[framesep=0pt]{$+Q$}}
\end{pspicture*}}
%%%
\rput[bl](-5,-3){\figure}
\psline{->}(-1.8,3)(-2,2.5)(-1.6,2.1)
\uput[90](-1.8,3){L\'{i}nea de fuerza}
\psline{->}(1.9,3.3)(1.4,3)(1.3,2.3)
\uput{2pt}[80](1.9,3.3){Superficie equipotencial}
\end{pspicture}

\end{document}

我想使用 linestyle=dashed 作为 \psEquipotential 的可选参数，但它不起作用。它的结果如下：

帮助！ ...

附加：

\documentclass[12pt,pstricks,border=10pt]{standalone}

\usepackage{pst-electricfield}
\begin{document}
\begin{pspicture}(-5.5,-5.5)(5.5,5.5)
\psset{unit=1.25cm}
\def\figure{\begin{pspicture*}(-4,-4)(4,4)
\psframe*[linecolor=green!20](-4,-4)(4,4)
\psgrid[subgriddiv=0,gridcolor=lightgray,griddots=10]
\psElectricfield[Q={[1 -2 0][-1 2 0]},linecolor=red,N=21,Pas=0.0115]

\foreach \n in {0,1,2,3,8,19}{
    \psEquipotential[Q={[1 -2 0][-1 2 0]},Vmin=-\n,Vmax=-\n](-5,-5)(5,5)
    \psEquipotential[Q={[1 -2 0][-1 2 0]},Vmin=\n,Vmax=\n](-5,-5)(5,5)
}
{\psset{linestyle=none,fillstyle=solid}
\pscircle[fillcolor=white](-2.05,0){2mm}
\pscircle[fillcolor=white](1.98,0){2mm}
\pscircle*(2,0){1.1mm}}
\pscircle(-2,0){1.1mm}
\uput{.6pt}[135](-2,0){\tiny \pscirclebox*[framesep=0pt]{$+Q$}}
\uput{.6pt}[45](2,0){\tiny \pscirclebox*[framesep=0pt]{$-Q$}}
\end{pspicture*}}

\rput[bl](-4,-4){\figure}
\psline{->}(-.8,4)(-1,3.8)(-.5,3.4)
\uput[90](-.8,4){L\'{i}nea de fuerza}
\psline{->}(-1,-4.2)(-1.7,-3.75)(-1.8,-3.2)
\uput{2pt}[-90](-1,-4.2){Superficie equipotencial}
\end{pspicture}

\end{document}