Coding a function to use the false position method to approximate roots

Question

Aaron Atkinson 2020-3-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/508413-coding-a-function-to-use-the-false-position-method-to-approximate-roots

评论： Walter Roberson 2021-12-26

Im trying to code together a function to approximate roots using the false psotion method. My current issues is that I can't understand how I should go about plugging in a polynomial into matlab in a standard form.

function [root, fx, ea, iter] = falsePosition(func, xl, xu, es, maxit, varargin)
%falsePosition finds the root of a function using false position method
%please input the func value in this format ((8x^4)-(2x^2)+x)---->[8 0 -2 1]
if nargin <3
    error('3 or more arguements required')
elseif nargin<4
    es=.0001;
    maxit=200;
end
plop=1;
for iter= 1:maxit
    if plop==1;
    root1= xl-(((polyval(func,xl))*(xu-xl))/((polyval(func,xu))-(polyval(func,xl))));
    xu=root1;
    plop=2;
    ea=10000000;
    elseif ea>es
        root2= xl-(((polyval(func,xl))*(xu-xl))/((polyval(func,xu))-(polyval(func,xl))));
        ea=((root2-root1)/root2)*100;
        xu=root2;
    else
        break
    end
    
    
    
    
end

I need to be able to plug in xu and xl into the equation, and I need to be able to plug the equation into the function in the form of ((3*x^3)+(8*x^2)*1) and not in the form of an array as [3 8 1]

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Aaron Atkinson 2020-3-1

I think I need to clarify, the primary issue I am having is translating the entered equation into something usable by matlab, how should I do this?

Walter Roberson 2021-12-26

((8x^4)-(2x^2)+x) should be [8 0 -2 1 0] not [8 0 -2 1] -- the 0 at the end is the constant coefficient.

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Answer 1

darova 2020-3-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/508413-coding-a-function-to-use-the-false-position-method-to-approximate-roots#answer_418081

在 MATLAB Online 中打开

try matlabFunction

str = input('enter a function:\n');
f = matlabFunction(str);

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aisha azawe 2021-12-25

f(x) = 10 * cos(x) + x^2 *sin(x) - 2

Walter Roberson 2021-12-26

在 MATLAB Online 中打开

@aisha azawe

f = @(x) 10 * cos(x) + x.^2 .* sin(x) - 2

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