Can anyone tell me why I'm getting an error here? "xold=xnew;'' is giving me an error in this statement and I'm not sure why.

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Brendan
Brendan 2023-2-22
回答： KSSV 2023-2-22
clear all
close all
clc
% Problem 6.7
while (1)
fx=@(x) x.^3-6*x.^2+11*x-6.1;
% Using the Modified Secant Method
xold=3.5;
d=0.01;
% Iteration 1
xold=xnew;
xnew=xold-d*xold*fx(xold)/(fx(xold+d*xold)-fx(xold));
ea=abs((xnew-xold)/xnew)*100;
% Iteration 2
xold=xnew;
xnew=xold-d*xold*fx(xold)/(fx(xold+d*xold)-fx(xold));
ea=abs((xnew-xold)/xnew)*100;
% Iteration 3
xold=xnew;
xnew=xold-d*xold*fx(xold)/(fx(xold+d*xold)-fx(xold));
ea=abs((xnew-xold)/xnew)*100;
fprintf('The root using 3 iterations of Modified Secant Method is %8.4f with an approximate relative error of %6.3e\n',xnew,ea)
end

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采纳的回答

KSSV
KSSV 2023-2-22
These lines:
xold=3.5;
d=0.01;
% Iteration 1
xold=xnew;
xnew=xold-d*xold*fx(xold)/(fx(xold+d*xold)-fx(xold));
will obviously thrwo an error becuase xnew is a new variable and it is not defined. You need to either comment this line or you may need to move to the next line. After calculating xnew then save xnew to xold.

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