/span> n==1,
0063       xp=(x(3:nn)-x(1:nn-2))./(t(3:nn)-t(1:nn-2));
0064       yp=(y(3:nn)-y(1:nn-2))./(t(3:nn)-t(1:nn-2));
0065       <span class="comment">%xpp=x(1:nn-2)+x(3:nn)-2*x(2:nn-1);</span>
0066       <span class="comment">%ypp=y(1:nn-2)+y(3:nn)-2*y(2:nn-1);</span>
0067       xpp=(x(3:nn)-x(2:nn-1))./(t(3:nn)-t(2:nn-1));
0068       xpp=xpp-(x(2:nn-1)-x(1:nn-2))./(t(2:nn-1)-t(1:nn-2));
0069       xpp=xpp./(t(3:nn)-t(1:nn-2))/2;
0070       ypp=(y(3:nn)-y(2:nn-1))./(t(3:nn)-t(2:nn-1));
0071       xp