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From: | Carlo de Falco |
Subject: | Re: Splines |
Date: | Wed, 1 Oct 2008 12:15:34 +0100 |
On 01/ott/08, at 11:55, Jaroslav Hajek wrote:
On Wed, Oct 1, 2008 at 12:44 PM, Carlo de Falco <address@hidden > wrote:interp1(x, y, 'cubic') is just a wrapper to pchip which does piece- wise cubic hermite interpolation the matlab help page for pchip contains a detailed comparison of pchip and spline, I think the algorithms in octave are the same as in matlab...On 01/ott/08, at 10:56, Jaroslav Hajek wrote:The interp1 functions *are* using splines when you specify "cubic" interpolation.not really, try...x = sortrows (rand(10,2)); xsp = linspace(min(x(:,1)), max(x(:,1)), 100); plot(x(:,1),x(:,2),'x', xsp, interp1(x(:,1), x(:,2), xsp, 'cubic'), xsp,spline(x(:,1), x(:,2), xsp))OK, 'spline' was what I meant, but I think that even the 'cubic' method uses some kind of spline, though probably it doesn't ensure smoothness.
BTW there are different kinds of splines, tryplot(x(:,1),x(:,2),'x', xsp, interp1(x(:,1), x(:,2), xsp, 'spline'), xsp, ppval(catmullrom(x(:,1), x(:,2)), xsp),'g-')
to see how catmullrom differs from the default not-a-knot spline.For this particular application I think the less oscillatory behaviour makes catmullrom preferable over spline
c.
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