Need A Newton Raphson matlab function

Question

i have a polynomial f(x)= x^3-a and i need its matlab function with parameters

function [x,err]=cubic1(a,xinit,eps) where xinit: Initial approximation eps: iterations are performed until approximate error is less than this number x: Root approximations of the function, and it is an array. relerr: Approximate errors corresponding to the iterations and it is an array.

do you have any idea ?

Answer 1

function [x,err] = cubic1(f,df_dx,x0,eps)
   err = Inf;
   x = x0;
   while abs(err) > eps
      x_old = x;
      x = x_old - f(x_old)./df_dx(x_old);
      err = x - x_old;
   end

To call the cubic1 function,

a = 1; % you can change a
f = @(x)(x.^3-a);
df_dx = @(x)(3*x.^2);
x0 = 1;
eps = 1e-7;
[x,err] = cubic1(@f,@df_dx,x0,eps);