三次样条插值
n=2;a = polyfit(y,x,2);
a'
x1 = a(1).*y.*y + a(2)*y + a(3);
figure(1)
plot(y, x, 'b.')
hold on
plot(y, x1,'r.')
hold off;
%%
A = [534.0 28965.7 1.60425e+006
28965.7 1.60425e+006 9.02824e+007
1.60425e+006 9.02824e+007 5.14776e+009];
B = [1840.57
99683.1
5.50671e+006];
a = inv(A)*B
A1 = [length(y), sum(y), sum(y.^2);
sum(y), sum(y.^2), sum(y.^3);
sum(y.^2), sum(y.^3), sum(y.^4);];
B1 = ;
a = inv(A1)*B1
x1 = a(3).*y.*y + a(2)*y + a(1);
figure(2)
plot(y, x, 'b.')
hold on
plot(y, x1,'r.')
hold off;
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