Decreasing varible into a loop

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Miguel Angel Villegas Hernandez 2021-7-20

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https://ww2.mathworks.cn/matlabcentral/answers/882178-decreasing-varible-into-a-loop

评论： Steven Lord 2021-7-20

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Hello

I'm new programming and I have to sove this.

I Have to decrease one varible using i=0 and increasing by 1, i=i+1, but at same time I have another expression that depends of "i" and i need to drecreasing that varible, let you show:

i = 0;
x = b;
Fx = Fb;
Ek = abs(xe-x);
EA = Ek/Ek+1;     %Here I've to solbe it
while 1    
    DeltaX = -Fx/(Fb-Fa)*(b-a);
    x = x+DeltaX;
    Fx = f(x);
    Ek = abs(xe-x);;    %Here I've to solbe it
 disp ([i a b x Fx DeltaX Ek ]);
       if(abs(DeltaX)<Tolerancia && abs(Fx)<Tolerancia)||i >=n
          break;
        end
    a = b;
    Fa = Fb;
    b = x;
    Fb = Fx;
    i = i+1;
 end

the equation is:

EA = Ek / E_k-1 it must be E_0/E_1 i =0 at the same time k = 2

Thanks

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Miguel Angel Villegas Hernandez 2021-7-20

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This is my code

f=@(x)x^3-3*x-2
function [Raiz,Iter,Error] = Secante(f,a,b,Tolerancia,IterMax);
xe = -1;      %scalar constant
x = a;
Fa = f(a);
x = b;
Fb = f(b);
  if abs(Fa) < abs(Fb)
    t = a;
    a = b;
    b = t;
    t = Fa;
    Fa = Fb;
    Fb = t;
  end
printf('Calculo de la raiz por el metodo de la secante\n i    a     b    x     Fx    DeltaX   Ek  \n');
i = 0;
x = b;
Fx = Fb;
Ek = abs(xe-x);   % Ek=abs(-1- x(i))
%here I want to introduce EA=Ek(i)/Ek(k-1),where "k" is another kund of counter linked with "i" counter
% it must be i=0 at same time k=2 to get Ek(0) / Ek(1), Ek(1) / Ek(2) 
while 1    
    DeltaX = -Fx/(Fb-Fa)*(b-a);
    x = x+DeltaX;
    Fx = f(x);
    Ek = abs(xe-x);
 disp ([i a b x Fx DeltaX Ek ]);
       if(abs(DeltaX)<Tolerancia && abs(Fx)<Tolerancia)||i >=IterMax
          break;
        end
    a = b;
    Fa = Fb;
    b = x;
    Fb = Fx;
    i = i+1;
 end
Raiz = x;
    if abs(DeltaX)<Tolerancia && abs(Fx)<Tolerancia
      Error = 0;
    else
      Error = 1;
    end
end