[pstricks] a problem with \psplotDiffEqn

[Andrzej J. Maciejewski]

Hi all,
I tried to use \psplotDiffEqn. In a simple example:
\documentclass{article}
\usepackage{pstricks-add}
\begin{document}
%
\def\Func{ neg }
\psset{unit=1cm}
%
\psset{method=rk,plotpoints=40,linecolor=blue,linewidth=0.5pt}
  \psset{whichabs=0,whichord=1}
\begin{pspicture}(-4,-2.5)(4,2.5)
\psplotDiffEqn{0}{1}{0 0.1}{\Func}
\end{pspicture}
\end{document}

latex gives no error however gv gives the following message
Error: /undefined in F2
Operand stack:
   0.0   --nostringval--   F1
Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--
--nostringval--   2   %stopped_push   --nostringval--   --nostringval--
--nostringval--   false   1   %stopped_push   1   3   %oparray_pop   1   3
%oparray_pop   1   3   %oparray_pop   1   3   %oparray_pop   .runexec2
--nostringval--   --nostringval--   --nostringval--   2   %stopped_push
--nostringval--   --nostringval--
Dictionary stack:
   --dict:1125/1686(ro)(G)--   --dict:0/20(G)--   --dict:78/200(L)--
--dict:175/300(L)--   --dict:38/200(L)--   --dict:104/200(L)--
Current allocation mode is local
Last OS error: 2
GPL Ghostscript 8.54: Unrecoverable error, exit code 1

I have installed new pstricks-add, pst-func,  xvalkey and put *.pro files in
an appropriate place.

I will be thankful for a help.

-Andrzej
-- 
Andrzej J. Maciejewski                       Institute of Astronomy
tel. +48 68 328 30 21                        University of Zielona Góra
fax. +48 68 328 73 60                       Podgórna 50, 65-246 Zielona Góra
http://astro.ia.uz.zgora.pl/~maciejka/    POLAND
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