# [pstricks] PSTricks Digest, Vol 90, Issue 8

mathias legrand legrand.mathias at gmail.com
Sun Jul 11 18:53:17 CEST 2010

>> Thanks, I see that the Derive and sum commands can be of great help.
>> Anyway, is postscript aware
>> of recursive statements? Most of the polynomials of interest are defined
>> as, for instance:
>> P_n(x)=xP_{n-1}(x)+P'_{n-1}(x)
>> with some initial P_0(x) and P_1(x) polynomials.
>>
> no, you have to define your own function. However,
> it is not too difficul

Here is what I could do:

\psset{xunit=3,yunit=2}
\def\in{7}
\begin{pspicture}(-1.1,-1.1)(1.1,1.1)
\psclip{\psframe[linestyle=none](-1.1,-1.1)(1.1,1.1)}
\psplot[linewidth=1pt,algebraic=true,linecolor=red]{-0.5}{0.5}{Derive(\in,((x^2-1)^\in))/((2^\in)*fact(\in))}
\endpsclip
\psframe(-1.01,-1.01)(1.01,1.01)
\end{pspicture}}

Anyway, for \in higher than 7, it crashes. Any idea why ? Otherwise, I
am pretty happy with it.