Using Secant Method...issue with arctanx

Question

Drake 2013-10-6

0
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https://ww2.mathworks.cn/matlabcentral/answers/89334-using-secant-method-issue-with-arctanx

编辑： Matt J 2013-10-6

I'm using secant method, I've done previous problems with the same setup of x2 = ..., but when I'm using arctan(x) as the function it tells me there is an error with the x2 = ... line (inside for loop). I have no idea why.

f = @(x) arctan(x);
format long
maxN = 10;
x0 = 1; 
x1 = -0.5;
r = 0; %know r=0 in advance
Err = .0000001; %max error
for i = 1:maxN     
    x2 = x1 - f(x1)*(x1-x0)/(f(x1)-f(x0))
    en1 = r - x2; %e_n+1
    en = r - x1; %e_n
    enm1 = r - x0; %e_n-1
    ratio = en1/(en*enm1)
    if abs((x2-x1)/x1) < Err
        r2 = x2; %root
        f(r2)
        break
    end    
    x1 = x0
    x0 = x2
end