Spline with clamped end conditions using griddedInterpolant

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John Billingham
John Billingham 2022-12-22
评论： John Billingham 2022-12-22
I can create a piecewise polynomial spline with clamped end conditions from vectors x and y using
pp = spline(x,[dy1 y dy2])
where dy1 and dy2 are the required slopes. How can I do this using griddedInterpolant?
fy = griddedInterpolant(x,y,'spline')
is the knot-a-knot spline. Can I not clamp the end points?

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回答（1 个）

John D'Errico
John D'Errico 2022-12-22
编辑：John D'Errico 2022-12-22
You cannot do so. There is no capability for that in griddedInterpolant. But I fail to see the problem. Just use spline, which DOES allow that option. Then you can interpolate the spline you have created as you wish. WTP?
  2 个评论
John Billingham
John Billingham 2022-12-22
Sorry, I should have added that griddedinterpolant seems to be much faster than ppval, and it's this speed that I'm after for a clamped spline.
John Billingham
John Billingham 2022-12-22
Ran in:
x = linspace(0,1,100); y = rand(1,100);
x1 = rand(1,100);
ppx = spline(x,y);
fx = griddedInterpolant(x,y,'spline');
tic
for k = 1:100000
y1 = ppval(ppx,x1);
end
toc
Elapsed time is 1.429425 seconds.
tic
for k = 1:100000
y1 = fx(x1);
end
toc
Elapsed time is 0.300864 seconds.
This makes a considerable difference for what I'm trying to do.

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