New to MATLAB - trying to write bisection method?

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AM 2013-12-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/109827-new-to-matlab-trying-to-write-bisection-method

评论： Walter Roberson 2020-11-9

Hello, I'm brand new to MATLAB and am trying to understand functions and scripts, and write the bisection method based on an algorithm from our textbook. However, I'm running into problems. Could anyone help me please?

Here is my code:

function [f] = Bisection(a,b,Nmax,TOL)
f = x^3  - x^2 + x;
i=1;
BisectA=f(a);
while i <= Nmax
    p=a+(b-a)/2;
    BisectP=f(p);
    if BisectP == 0 || (b-a)/2 < TOL        
        disp('p');
    end
    i=i+1;
    if BisectA*BisectP > 0
        a=p;
        BisectA=BisectP;
    else
        b=p;
    end
end
disp('Method failed after num2str(Nmax) iterations, Nmax=', Nmax);

Thanks.

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youcef mokrane 2020-11-9

编辑：Walter Roberson 2020-11-9

在 MATLAB Online 中打开

x=4:4.7
f=tan(x)-x
a=4
b=4.7
fa=tan(a)-a
fb=tan(b)-b
n=1
n0=5000
             while n<5000
                   p=(a+b)/2
                   fp=tan(p)-p
                  n=n+1
                     if fa*fp>0
                         a=p
                       else 
                         b=p
                    end
           end

Walter Roberson 2020-11-9

Why are you bothering to do x=4:4.7 ? The default increment for the colon operator is 1, so 4:4.7 is the same as 4:1:4.7 which is just going to be 4 .

Why are you assigning to n0 when you do not use it?

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采纳的回答

Walter Roberson 2013-12-15

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/109827-new-to-matlab-trying-to-write-bisection-method#answer_118453

编辑：Walter Roberson 2013-12-16

在 MATLAB Online 中打开

Your line

f = x^3 - x^2 + x;

does not define a function. Try

f = @(x) x^3 - x^2 + x;

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A_J Khan 2017-9-18

编辑：Walter Roberson 2017-9-18

在 MATLAB Online 中打开

   function p = bisection(f,a,b)
      |
  Error: Function definitions are not permitted in this
  context.

I have this error with above code....???

Walter Roberson 2017-9-18

You can never define a function at the command prompt: you have to store a function inside a .m file; in this case, bisection.m

In versions up to R2016a you cannot store a function inside a script file (a .m file that does not start with the word "function" or "classdef"). That changed in R2016b.

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