Why won't my code run.

Question

me 2015-9-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/243204-why-won-t-my-code-run

编辑： James Tursa 2015-9-16

在 MATLAB Online 中打开

My code keeps giving me the error

Error using bisec (line 5) Not enough input arguments.

I don't understand what am doing wrong.

function m = bisec(f, low, high, tol)
disp('Here Bisection Method Starts: ');
% evaluating both intervals
y1 = feval(f, low);
y2 = feval(f, high);
i = 0;
% error handling
if y1 * y2 > 0
    disp('sorry not correct values given...');
    m = 'Error'
    return
end
% start bisection method until nearer to zero
while (abs(high - low) >= tol)
    i = i + 1;
    % Getting new value to test for root
    m = (high + low)/2;
    y3 = feval(f, m);
    if y3 == 0
        return
    end
      % Update limits
      if y1 * y3 > 0
          low = m;
          y1 = y3;
      else
          high = m;
      end
  end
% Printing final results
w = feval(f, m);
fprintf('\n x = %f produces f(x) = %f \n %i iterations\n', m, y3, i-1);
fprintf(' Approximation with tolerance = %f \n', tol);

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Answer 1

James Tursa 2015-9-16

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/243204-why-won-t-my-code-run#answer_192500

编辑：James Tursa 2015-9-16

How are you calling bisec? From the error message, it looks like you are not providing all of the inputs. E.g., if you only did bisec(@myFunction) then that would only be one input, and then bisec would complain when it tried to use low because it wasn't input to the function.

A nit: If y1 or y2 start out exactly 0, your code doesn't detect this immediate solution.

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me 2015-9-16

also how do i call the function if f=sin(x)+x

James Tursa 2015-9-16

编辑：James Tursa 2015-9-16

在 MATLAB Online 中打开

You don't need to test for low>high since your code will work regardless of the order they are input (try it!). But testing for low==high makes sense. Note that if low==high then sign(y1)==sign(y2) will also be true, so that implies sign(y1)*sign(y2)==1. So the 2nd test covers the case for low==high. So maybe something like this:

if( sign(y1)*sign(y2) == 1 )
    error('Invalid inputs. low==high or signs of function results are the same');
end

But keep in mind my earlier comment about y1==0 or y2==0 being detected for immediate solution. Also note that I used the "error" function. This is the normal way for a function to stop with an error as it forces the calling function to either stop or to deal with the error. Doing "m = 'Error'" as you are currently doing simply returns a value back to the caller that may in fact get used downstream by the caller as an actual valid result, producing garbage results. It relies on a user actually looking at the screen to tell that something went wrong. This is not a good way for your function to report an error since it makes unsafe assumptions about the caller.

To use f=sin(x)+x you could do this (anonymous function handle):

f = @(x)sin(x)+x

Then pass in f as the first argument. E.g., see this link:

http://www.mathworks.com/help/matlab/matlab_prog/anonymous-functions.html?searchHighlight=anonymous%20function

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