I need to use Newton's method to solve f(x). Can any one tell me what's wrong of my code and how to improve it.

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Chun Kit NG
Chun Kit NG 2022-2-9
回答： David Hill 2022-2-9

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回答（2 个）

Yongjian Feng
Yongjian Feng 2022-2-9
what i s your dx?
David Hill
David Hill 2022-2-9
a=1:4;
tiny=1e-10;
x=ones(size(a));%this will not work well for the initial guess
for k=1:length(a)
f=@(x)tan(x)+a(k)*sin(x)./x;
fp=@(x)sec(x)^2-a(k)*sin(x)/(x^2)+a(k)*cos(x)/x;
rat=1;
while rat>tiny
dx=f(x(k))/fp(x(k));
x(k)=x(k)-dx;
rat=abs(dx/x(k));
end
end
If you look at your plot, you will realize that there are lots of crossings. Your initial guess for x must be close to the crossing you want.

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