Bisection Method Issues/Help

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SB 2012-11-19

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https://ww2.mathworks.cn/matlabcentral/answers/54150-bisection-method-issues-help

Hi people, I'm having a bit of an issue with my Bisection Method Algorithm, which I understand conceptually, but it doesn't quite work with my code. My outputs are the final root, absolute value of the function at the root, number of iterations and all the midpoints generated through each iteration. Here's my code so far:

    % function [r,rHist,N,fRoot] = bisectionE7(fHan,xL,xR,fTol,iterMax)
k= 0; % initialize iteration counter
fxL = feval(fHan,xL);
fxR = feval(fHan,xR);
sfxL = sign(fxL);
sfxR = sign(fxR);
if (sfxL*sfxR > 0)
  r=[];
  rHist=[];
  N=[];
  fRoot=[];  
end
while (k <= iterMax)
  % use midpoint as the iterate  
  c = (xL+xR)/2;
  fc = feval(f,c);
  sfc = sign(fc);
  if ((xR-xL)<2*fTol | fc == 0)
    x = c;
    return 
  elseif (sfxL*sfc < 0)
    xR = c;
  else
    xL = c;
  end
  k = k+ 1;
end
% if this while loop terminates before returning the root
disp(' max number of iterations reached ... ')
  x = xL;

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John Petersen 2012-11-20

Okay, so the code doesn't work. What is your question? Where does it fail? What parts work? Try bisecting the problem to help you find where you are having a problem and then someone will be more able and willing to help.

SB 2012-11-21