I got an error of my code. This code is Newton's method. Can anybody help with me?? Thank you!!

error occur: Newton (line 3)
[x,y] = Newton(f, df, 0.5, 0.00001, 5);

f = inline('x.^3-3*x.^2+4/3');
df = inline('3*x.^2-6*x');
[x,y] = Newton(f, df, 0.5, 0.00001, 5);
% function [x, y] = Newton(fun, funpr, x1, tol, kmax)
% Input:
%   fun   function (inline function or m-file function)
%   funpr derivative function (inline or m-file)
%   x1    starting estimate
%   tol   allowable tolerance in computed zero
%   kmax  maximum number of iterations
%output
%   x     (row) vector of approximations to zero
%   y     (row) vector fun(x)
x(1)= x1;
y(1) = feval(fun, x(1));
ypr(1) = feval(funpr, x(1));
for k = 2: kmax
    x(k) = x(k-1)-y(k-1)/ypr(k-1); y(k) = feval(fun, x(k));
    if abs(x(k)-x(k- 1)) <tol
        disp('Newton method has converged?');    break; 

      end
      ypr(k) = feval(funpr, x(k));
      iterk; 
  end
  if (iter >= kmax)
      disp('zero not found to desired tolerance');
  end
  n = length(x);
  k = 1:n;
  out = [k'  X'  y'];
  disp('              step            x           y')
  disp(out)

Answer 1

[Walter Roberson]

Put the lines

f = inline('x.^3-3*x.^2+4/3');
df = inline('3*x.^2-6*x');
[x,y] = Newton(f, df, 0.5, 0.00001, 5);

into a file named Newton_test.m

Then in Newton.m have the rest of your code with the 'function' line not commented out.

function [x, y] = Newton(fun, funpr, x1, tol, kmax)
% Input:
%   fun   function (inline function or m-file function)
%   funpr derivative function (inline or m-file)
%   x1    starting estimate
%   tol   allowable tolerance in computed zero
%   kmax  maximum number of iterations
%output
%   x     (row) vector of approximations to zero
%   y     (row) vector fun(x)
x(1)= x1;
y(1) = feval(fun, x(1));
ypr(1) = feval(funpr, x(1));
for k = 2: kmax
    x(k) = x(k-1)-y(k-1)/ypr(k-1); y(k) = feval(fun, x(k));
    if abs(x(k)-x(k- 1)) <tol
        disp('Newton method has converged?');    break; 

        end
        ypr(k) = feval(funpr, x(k));
        iterk; 
    end
    if (iter >= kmax)
        disp('zero not found to desired tolerance');
    end
    n = length(x);
    k = 1:n;
    out = [k'  X'  y'];
    disp('              step            x           y')
    disp(out)

And to run this you would execute the file Newton_test

[SEUNGMYEONG CHOO]

I followed your instruction, but there is an error again. Can you give me more specific solution? Thank you very much!!

[Walter Roberson]

You need to tell us what the error message is and show us exactly where it is occurring.