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How to differentiate a cubic spline

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MeEngr
MeEngr 2015-2-10
评论： MeEngr 2015-2-10
Hi all.
I'm plotting the position of a particle vs time using a cubic spline as follows:
xx = csapi(t, pos);
fnplt(xx);
Here, t and pos are both vectors.
I now need to plot the velocity vs time for this particle. My question is, how do I differentiate a cubic spline? Any help would be appreciated.

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回答（1 个）

John D'Errico
John D'Errico 2015-2-10
Simple enough to do by differentiating each polynomial segment.
That is, if we have
pp = csapi(t,pos);
Then for a cubic spline in pp form, this will suffice:
ppd = pp;
ppd.coefs = ppd.coefs*diag([3 2 1],1);
  1 个评论
MeEngr
MeEngr 2015-2-10
Thanks, John. I'm sorry, but I'm still confused.
What exactly are we achieving using these two commands and how do I plot the velocity? I'm trying to look this up online and in Matlab's documentation but I'm not getting anything.

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