This is code for Modified Regula Falsi method for finding roots. Something in here is preventing the if statements from executing properly.

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Jay Gersten 2016-9-28

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https://ww2.mathworks.cn/matlabcentral/answers/304799-this-is-code-for-modified-regula-falsi-method-for-finding-roots-something-in-here-is-preventing-the

评论： Jay Gersten 2016-11-8

function  ModRegFal = ModRegFal(a, b, n) 
format long;
a = input('Enter a value for lower boundary a: ');
b = input('Enter a value for upper boundary b: ');
n = input('How small should should the error be (to what -power)? ');
if (f(a)*f(b) > 0 )
    disp ('Invalid values of a and b. Program Closing')
    return;
end;
F = f(a);
G = f(b);
w0 = a;
while (1)
wn = (G*a-F*b)/(G-F);
disp([a b wn w0]) %%just checking where the values are, and it they look correct
if f(a)*f(wn) > 0 
   disp('ranif 1')%%just checking where the values are, and it they look correct
    b = wn;
    G = f(wn);
        if f(w0)*f(wn) > 0 
            F = F/ 2; end;
        disp('ranif 2')%%just checking where the values are, and it they look correct
        disp([a b wn w0])%%just checking where the values are, and it they look correct
else 
    a = wn;
    F = f(wn);
        if f(w0)*f(wn) > 0 
           disp('ranif 3')%%just checking where the values are, and it they look correct
           disp([a b wn w0])%%just checking where the values are, and it they look correct
            G = G/ 2; end;
end
disp([a b wn w0])
if (abs((wn - w0)/wn) < 0.5*10^-n)
    disp ('The root is: ')
    disp (wn)
    break; 
else
    w0 = wn;
end
end

I wrote a separate scrip with the function y = f(x) y = x^2 - 2;

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Geoff Hayes 2016-9-28

Jay - why do you pass in the input parameters a, b and n only to overwrite them with user input? How or where is f defined because the above code would fail with an error for this undefined function?

Please provide a working sample of code and include your steps on calling this function.

Jay Gersten 2016-11-8