Decreasing varible into a loop

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

[Jan]

All we see is some code, which does not run. Several variables are not defined. You did neither mention in the question nor in the comments of the code, what you want to achieve. There readers might be able to guess, what you want, but this is not an efficient way to solve a problem.

• Start with inserting some comments, which explain clearly, what you want to achieve.
• Then define all missing variables

[Steven Lord]

Can you define variables with numbered names like E_1, E_2, E_3, ... which is what I think you're trying to do? Yes.

Should you do this? Generally we recommend against it.

[Miguel Angel Villegas Hernandez]

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

I hope be explicit.

Thanks

[Steven Lord]

There's no element 0 in an array in MATLAB, so E(0) will error if E is a regular numeric array.