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% page 151 3
5 h$ Y% b1 U! q( h0 a' T% 写出一个插值多项式$ V+ I* c8 r1 \% T* o
% input :vector(x,y),interpolation point x0. l' x8 q# f& J
% output:the result at x = x0% y1 S' S+ J6 b5 h5 a( u; m4 i" l: r
function y0 = page_157_1(x ,y,x0)
- K! J: M- Q+ |1 Zformat long+ Y7 l$ T% p* g1 `
n = length(x);
" h- U5 }+ B& B. {$ }" c, mfor j = 1:n %fill in y colum of Newton triangle! x, M' i$ C! K! l: L$ L
v(j,1) = y(j);# @9 V4 L8 r4 c+ m( x& }
end) t2 I5 ^5 \! k9 O' {. F$ D
for i = 2:n %for colum i1 q7 N% r) ^4 w9 Z" N# Z
for j = 1:n+1-i %fill in colum from top to bottom
& ~$ L. N1 _" _0 V v(j,i) = (v(j+1,i-1) - v(j,i-1))/(x(j+i-1)-x(j));% _9 _9 q" S4 }8 v! L0 I$ v
end' R, G Z" I& }% P
end
( q) h+ Y1 ?' J: G* {for i = 1:n) b$ L: i, r7 e! W% D
v(i) = v(1,i); %read along top of triangle
' f8 U7 k/ c& P- |5 T1 G$ @. uend %output coefficients
! ?7 k/ c, X- Xy0 = v(n)*(x0 - x(n-1)) + v(n-1); %initial nest! S+ c/ E S" h
for i = 1:n-2 %use nest. Z3 n2 E) n: G O+ N* n
y0 = y0*(x0 - x(n-1-i)) + v(n-1-i);
0 _' {' d- p/ W5 `end
& @6 E1 ^, N F M |
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