Can someone close this question?

Question

Aviv Elor 2015-10-14

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评论： Rena Berman 2017-1-12

I need help with matlab. Why won't the while loop end when xstar = .7931? I've ran the code and xstar eventually does repeat at .7931, but it gets caught in an infinite loop. Could someone explain what's wrong with my code? Thanks

%The purpose of this script is to show the fixed point of the equation below
%The task is to show that the following equation has x* = .7931
%To so such we run the equation until we reached a steady number
%equation: X(n+1) = cos(Xn)
format compact %to look pretty and end my OCD
xstar = 0;
i = 1;
x = 1:100;
while xstar ~= .7931  %while x does not = x* (x* is given above)
x(i+1) = cos(x(i)) % X(n+1) = cos(Xn), implemented through the loop
i = i + 1 %increase increment 
xstar = x(i)
end
display('When following the equation of X(n+1) = cos(Xn)...')
display(['X*', ' is ', num2str(xstar), ' after ', num2str(i), ' intervals'])

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John D'Errico 2015-10-15

When you edit away the text of your question, you insult the person who bothered to waste their time on you.

Why would you do this? Why would you make their answer useless for ANYONE else in the world who might have a similar problem?

Rena Berman 2017-1-12

(Answers Dev) Restored question.

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Answer 1

Niko 2015-10-14

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https://ww2.mathworks.cn/matlabcentral/answers/248666-can-someone-close-this-question#answer_195986

在 MATLAB Online 中打开

First of all, it's .7391, not .7931. The problem with your code is that your value of xstar will not be exactly equal to .7391 (which is a rational number, hence generally not a solution to a transcendental equation), so there's bound to be some error in the result.

To fix it, change

while xstar ~= .7931

to

while abs(xstar-.7391)>1E-4

and it'll work.