[pstricks] \psplotDiffEqn (pstricks-add)
Alexander Grahn
A.Grahn at fzd.de
Tue Jun 2 16:31:24 CEST 2009
Hi,
I want to translate the set of differential equations of the 'spiral of
cornu' example from the pstricks-add manual, Section 36.2 from algebraic
into Postscript syntax.
>From the Postscript reference I know that the sin and cos operators
want angles in degrees as their argument. Hence, I have to multiply the
arguments of sin and cos, as given in Eqs. (4) and (5) on Page 170 of
pstricks-add-doc.pdf, by 180/Pi which led me to the following formulation:
\documentclass{article}
\usepackage{pstricks-add}
\begin{document}
\psset{unit=8}
\begin{pspicture}(1,1)\psgrid[subgriddiv=5]
\psplotDiffEqn[
whichabs=0,whichord=1,linecolor=red,method=rk4,
% algebraic=true,
plotpoints=500,showpoints=true
]{0}{10}{0 0}{
% %algebraic
% cos(Pi*x^2/2)|sin(Pi*x^2/2)
%Postscript
x dup mul 2 div 180 mul cos %% dx/dt
x dup mul 2 div 180 mul sin %% dy/dt
}
\end{pspicture}
\end{document}
However, the chart remains empty, no spiral to be seen. What is wrong
with the above code?
Thanks for your suggestions,
Alexander
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