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How to determine how a loop finishes

Asked by Chris on 18 Nov 2013
Latest activity Answered by Chris on 18 Nov 2013

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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Chris

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2 Answers

Answer by Image Analyst on 18 Nov 2013
Edited by Image Analyst on 18 Nov 2013
Accepted answer

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

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Image Analyst
Answer by Chris on 18 Nov 2013

Thank you very much, that helped a lot.

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Chris

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