Help with Newton's method function?

2016 11 20
1 个回答
更新时间：2016 11 20
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This is the function I've been making to run Newton's method, but I can't get it to work. Any help with what I might be missing? Thanks!
function xn = newtonmethod(f,fd,x0,tol)
xn=x0;
err=abs(f(xn)-0);
i=0;
while err>tol
i=i+1;
xnew=xn-(f(xn)/fd(xn));
err=abs(f(xnew)-0);
end

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回答（1 个）

Walter Roberson
Walter Roberson 2016-11-20

0 个投票

I suspect your
err=abs(f(xnew)-0);
should be
err=abs(f(xnew)-f(xn));
unless you know that your f() has a "right" value of 0.

2 个评论
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Lauren Hux
Lauren Hux 2016-11-20
It does. Do you see anything else wrong with the code?
Walter Roberson
Walter Roberson 2016-11-20
You do not update xn = xnew

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