spderiv.m

来自「一套从入门到精通的Matlab学习教材」· M 代码 · 共 43 行

function z=spderiv(x,y,xi)
%SPDERIV Cubic Spline Derivative Interpolation.
% YI=SPDERIV(X,Y,XI) uses cubic spline interpolation to fit the
% data in X and Y, differentiates the spline, and returns values
% of the spline derivatives evaluated at the points in XI.
%
% PPD=SPDERIV(PP) returns the piecewise polynomial vector PPD
% describing the cubic spline derivative of the curve described by
% the piecewise polynomial in PP. PP is returned by the function
% SPLINE and is a data vector containing all information to
% evaluate and manipulate a spline. 
%
% YI=SPDERIV(PP,XI) differentiates the cubic spline given by
% the piecewise polynomial PP, and returns the values of the
% spline derivatives evaluated at the points in XI.
%
% See also SPLINE, PPVAL, MKPP, UNMKPP, SPINTGRL

% D.C. Hanselman, University of Maine, Orono, ME 04469
% 1/27/95
% Copyright (c) 1996 by Prentice-Hall, Inc. 

if nargin==3
	pp=spline(x,y);
else
	pp=x;
end
[br,co,npy,nco]=unmkpp(pp);	% take apart pp
if nco==1|pp(1)~=10
	error('Spline data does not have the correct PP form.')
end
sf=nco-1:-1:1;							% scale factors for differentiation
dco=sf(ones(npy,1),:).*co(:,1:nco-1);	% derivative coefficients
ppd=mkpp(br,dco); 						% build pp form for derivative
if nargin==1
	z=ppd;
elseif nargin==2
	z=ppval(ppd,y);
else
	z=ppval(ppd,xi);
end