x = linspace(0,2*pi,4);
y = sin(x);
xx = linspace(0,2*pi,19);
yy1 = interp1(x,y,xx);
yy2 = spline(x,y,xx);
yy3 = spline(x,[0 y -1],xx);
yy4 = pchip(x,y,xx);
plot(x,y,'ko',xx,yy1,'k.',xx,yy2,'k--',xx,yy3,...
	'k-.',xx,yy4,'k-');













