clear all 
close all
%load some data
load linefit.dat
x=linefit(:,1);
y=linefit(:,2);
plot(x,y,'o')
xp=0:.1:7;

%how to use splines
yspline=spline(x,y);
yp=ppval(yspline,xp);
hold on
plot(xp,yp,'g')

yclamp=spline(x,[0 y.' 0]);
yc=ppval(yclamp,xp)
plot(xp,yc,'m')

yclamp2=spline(x,[-9 y.' 9]);
yc2=ppval(yclamp2,xp)
plot(xp,yc2,'k')