新手求助，求曲线长度的问题
 

x=[0.2, 4.96, 6.55, 9.71, 13.17, 16.23, 18.36, 20.53, 23.15, 26.49, 28.23, 29.1, 30.65, 30.92, 31.67, 33.03, 34.35, 35.01, 37.5];
y=[6.66, 5.28, 4.68, 5.19, 2.34, 6.94, 5.55, 9.86, 5.28, 3.87, 3.04, 2.88, 3.68, 2.38, 2.06, 2.58, 2.16, 1.45, 6];

plot(x,y,'k.','markersize',15);
axis([-5 40 0 45]);
grid;hold on [COLOR="SeaGreen"]%作点[/COLOR]

k=0.2:0.001:37.5;
u=spline (x,y,k);
plot(k,u); [COLOR="seagreen"]%三次样条插值拟合曲线[/COLOR]

p=sqrt(diff(k).^2+diff(u).^2);
L=sum(p) [COLOR="seagreen"]%求总曲线长[/COLOR]

[COLOR="seagreen"]%如何求每两点间的曲线长度？以数组的形式表示出来。谢谢啊很紧急[/COLOR]