don't know the problem in my while loop

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there is also another error idk about of :
Array indices must be positive integers or logical values.
Error in sym/subsref (line 890)
R_tilde = builtin('subsref',L_tilde,Idx);
iteration=0;i=1;
x=zeros(100,1);
syms f(x);
f(x) = input('donner une function : f(x)= ');
e = input('donner une la valuer de erreur : e = ');
x(1) = input('donner la valeur de depart : x1 = ');
while ( e < abs(x(i+1)-x(i)) )
iteration = iteration +1 ;
x(i+1)=x(i)-f(x(i))/diff(f(x(i)));
i=i+1;
end
disp('la value de x apartir de e est', x(i));
disp(iteration);

Accepted Answer

the cyclist
the cyclist on 1 Jan 2022
You initialize the value of i to be zero.
Then you try
x(i)
which is equivalent to
x(0)
which means you are trying to access the zeroth element of x. But MATLAB indexing begins at 1, not 0, so you get that error.
  8 Comments
the cyclist
the cyclist on 1 Jan 2022
OK. Is the following code equivalent to your example, and give the error you see?
I removed the input functions (because they won't work here), and I also used an anonymous function instead of the symbolic function (because I don't have that toolbox).
iteration=0;
i=1;
x=zeros(100,1);
% syms f(x);
% f(x) = input('donner une function : f(x)= ');
% e = input('donner une la valuer de erreur : e = ');
% x(1) = input('donner la valeur de depart : x1 = ');
f = @(x) x.^3 - 10;
e = 0.001;
x(1) = 3;
while ( e < abs(x(i+1)-x(i)) )
iteration = iteration +1 ;
x(i+1)=x(i)-f(x(i))/diff(f(x(i)));
i=i+1;
end
Error using /
Matrix dimensions must agree.
disp('la value de x apartir de e est', x(i));
disp(iteration);

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More Answers (1)

hamza kharbouch
hamza kharbouch on 1 Jan 2022
okey i did minor other simplifications and it's working now
thanks
i=1;
iteration=0;
f = @(x) cos(x);
df = @(x) -sin(x);
e = 0.00001;
x(1) = 3;
while ( e < abs(x(i+1)-x(i)) )
iteration = iteration +1 ;
x(i+1)=x(i)-f(x(i))/df(x(i));
i=i+1;
end
disp(iteration);
disp(x(i));

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