How to determine how a loop finishes

Question

Chris 2013-11-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/106541-how-to-determine-how-a-loop-finishes

回答： Chris 2013-11-18

Alright, so I have an assignment where I am to use the secant method to find the root of a function. I have the program written for the most part, and I'm able to find the root of a function no problem. However, I don't know how to have an output that can determine whether the loop finished because an answer was found, or if all the iterations were used and an answer was not located. I think I'm supposed to use an if/end or if/else kind of statement, but I'm not completely sure. I have the code listed below, any help would be greatly appreciated.

syms x
func=('x^2 - 4');
A=0; % A= x(k-1) 
B=10;% B= x(k) 
abs_err=0.00001;
n=5; %number of iterations 
f = inline(func);
C = B - ((B-A)/(f(B) - f(A)))*f(B); % C= x(k+1)
display(['   The function to be used is ' func])
fprintf('   The first guess, x(1) is equal to %g\n',A)
fprintf('   The second guess, x(2) is equal to %g\n',B)
fprintf('   The absolute approximate error, Ea, is equal to %g\n',abs_err)
fprintf('   The maximum number of iterations to conduct, n, is equal to %g\n',n)
disp(' ')
while abs(f(C)) > abs_err
    A=B;
    B=C;
    C= B - ((B-A)/(f(B) - f(A)))*f(B);
    n=n+1;
    if(n==1000)
        break
    end
end
disp('Outputs')
display(['   The root of the function = ' num2str(C)])

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Answer 1

Image Analyst 2013-11-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/106541-how-to-determine-how-a-loop-finishes#answer_115552

编辑：Image Analyst 2013-11-18

在 MATLAB Online 中打开

After the loop:

if n >= 1000
  message = sprintf('No solution found after %d iterations.', n);
  uiwait(warndlg(message));
else
  message = sprintf(('Outputs\n   The root of the function = %f\n', C);
  uiwait(warndlg(message));
end