Dear Andrzej, please try : \psset{method=rk4,plotpoints=40,linecolor=blue,linewidth=0.5pt} %\psset{whichabs=0,whichord=1} \begin{pspicture}(-4,-2.5)(4,2.5)\psgrid \psplotDiffEqn{0}{4}{2}{\Func} % ^initial value \end{pspicture} Regards Dominique -- Les Galinières - 07460 St André de C. FRANCE-- tel: (+33)475.39.05.82