What is causing this to have an infinite loop??

2 次查看（过去 30 天）

Phi Tran 2018-3-2

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/385918-what-is-causing-this-to-have-an-infinite-loop

评论： Guillaume 2018-3-2

%testing our newton's method on a known problem
%we know the root is pi
p0 = 1;%initial guess
tol = 1e-8;
exact = 3.14159;%exact root
%enter function and its derivative
f = @(x) sin(x);
fp = @(x) cos(x);
%compare initial guess to exact root
diff = abs(p0-exact);
%iterate newton's method
while diff > tol
    p = p0 - f(p0)/fp(p0);
    diff = abs(p-exact); %stop when our iterate is close to the exact root, pi
    p0 = p;
end
%print the root to the screen
p

2 个评论
显示无隐藏无

KL 2018-3-2

编辑：KL 2018-3-2

If you have access to symbolic math toolbox, I'd suggest vpa/digits.

https://www.mathworks.com/help/symbolic/vpa.html https://www.mathworks.com/help/symbolic/digits.html

Guillaume 2018-3-2

Completely unrelated to the problem: it is not a good idea to name a variable diff as it will prevent you from using the very useful diff function.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Birdman 2018-3-2

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/385918-what-is-causing-this-to-have-an-infinite-loop#answer_308018

编辑：Birdman 2018-3-2

在 MATLAB Online 中打开

Add a condition to break out of the loop then the while condition is not satisfied as:

while diff > tol
    if ismembertol(diff,exact,tol)
       break;
    end
    p = p0 - f(p0)/fp(p0);
    diff = abs(p-exact); %stop when our iterate is close to the exact root, pi      
    p0 = p;
end