Newton's Method Help

Question

Kaeden Beaty 2021-2-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/743852-newton-s-method-help

评论： Alan Stevens 2021-2-12

I have a code that works for Newton's method, but I am trying to make it into an algorithm that takes an imput from the interval [a, b] instead of x0. In other words I guess the initial point is calculated inside of the cody using x0=(a+b)/2. Another thing I would like to do is insert an if statement into the main loop that breaks out of the loop if the x is outside of [a, b]. This is the original that works, but uses an input of x0.

function x=mynewton(f,df,x0,tol,maxiter)
x=x0;
xold=x
for i=1:maxiter
    x=x-f(x)/df(x)
  err(1)=abs(x-xold)
   xold=x
   if err(1)<tol
       break
   end
end

And then this is what I tried to do but there is an error

function x=mynewton2(f,df,x0,tol,maxiter)
x=(a+b)/2;
xold=x
for i=1:maxiter
    x=x-f(x)/df(x)
  err(1)=abs(x-xold)
   xold=x
   if err(1)<tol
       break
   end
       if x<a
           break
       end
           if x>b
               break
           end
   end
end