How is the Spline function different from the Interp1 function when using the Spline method?

Does anybody know why I would be getting different results from the Spline function vs. the Interp1 function using the Spline method? I have tried to look up if others have this problem but the only开发者_Python百科 thing that I can find is that the functions expect the inputs in different orders (i.e. column vs. row). The code that I am running is...

p1 = [20 40];    p2 = [200 500];    p3 = [400 300];    p4 = [600 500];
p = [p1; p2; p3; p4];

axis([0 1000 0 1000]); hold;
plot(p(:,1), p(:,2),'o')
x = linspace(0,1000,600);

%% 1
pp = spline(p(:,1),p(:,2));
yy = ppval(pp, x);
plot(yy,'r')

%% 2
y = interp1(p(:,1),p(:,2),x,'spline');
plot(x,y,'g')

If you look at the resulting plots, there is a large difference and I am unsure as to why that is. Any help would be appreciated!

You made a typing error in plotting the first method.

That should be:

%% 1
pp = spline(p(:,1),p(:,2));
yy = ppval(pp, x);
plot(x,yy,'r') %notice the x!

%% 2
y = interp1(p(:,1),p(:,2),x,'spline');
plot(x,y,'g')

Without that x parameter, the plot will take `x = 1:numel(yy)' on the x-axis of your plot, which causes the squeezed plot you had before.