how to use this m-file to solve an equation?

Question

Otto 2012-10-27

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回答： Onur Aytan 2015-10-24

Hi All,

I'm a very beginner in MATLAB. I've written a program using modified false position method to calculate positive x-value that satisfies x^10=1 equation but I don't know how to get this result using this m-file. should I use fsolve or some another command?

Here is the code;

function ModFalsePos=eqn(xl,xu,es,xr,ea)
f=@(x)x^10
xl=0
xu=1.3
es=0.01
fl=f(xl)
fu=f(xu)
while (1)
    xr=xu-fu*(xl-xu)/(fl-fu)
    xrold=xr
    fr=f(xr)
    if xr<0
    elseif xr>0
        ea=abs((xr-xold)/xr)*100
    end
    test=fl*fr
    if test<0
        xu=xr
        fu=f(xu)
        iu=0
        il=il+1
        if il>=2
            fl=fl/2
        end
    elseif test>0
        xl=xr
        fl=f(xl)
        il=0
        iu=iu+1
        if iu>=2
            fu=fu/2
        end
    else
        ea=0
    end
    if ea<es
        break
    end
end
ModFalsePos=xr
end

initial guesses are xl=0 and xu=1.3, is that code true or something wrong in this code too?

Thanks for any help!

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Jan 2012-10-27

编辑：Jan 2012-10-27

Hi Otto. Welcome to this forum. To make your code readable, you can apply a simple code formatting method: 1 empty line before and after the code, 2 leading spaces in each line.

Do you have the impression, that your code is wrong? If so, what detail let you assume this?

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Answer 1

Gang-Gyoo 2012-10-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/52026-how-to-use-this-m-file-to-solve-an-equation#answer_63510

在 MATLAB Online 中打开

This is the Bisection method for finding the solution

function test x= eqn(@(x)x^10-1,0,1.3,1e-6,50) end

function x2= eqn(fun,x0,x1,eps,nmax)
for i= 1: nmax
  x2= (x0+x1)/2;
  if abs(x2-x1) <= eps
    return;
    end
  fx0= fun(x0);
  fx2= fun(x2);
    if fx0*fx2 < 0
      x1= x2;
    else
      x0= x2;
    end
end
disp('Completed unsuccessfully');
end

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Otto 2012-10-28

Thank you for your interest, but solving this problem with modified false position method is mandatory. So, I've written this code using Modified false position algorythm but I don't know how to use it to solve x^10=1 and not sure if the code is correct.

Thanks for your interest again!

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Answer 2

Onur Aytan 2015-10-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/52026-how-to-use-this-m-file-to-solve-an-equation#answer_197221

Hello, I too need help for the same question, which is originally: f(x)=x^10-1, locate the root between x=0 and x=1.3 using the modified false position method. I worked on it but could not possibly run without any problem, I can't deal with programming stuff. It has a mind blowing complexity,:/ Please can anybody help for this problem as this question becomes more interesting for more people to be solved?