MATLAB: I’m not understanding why this error occurs: Error: Unexpected MATLAB expression

unexpected matlab expression

What i entered in console and received
 >> newton(x^3-x,3x^2-1,-1,1e-5,20)
  ??? newton(x^3-x,3x^2-1,-1,1e-5,20)
                    |
  Error: Unexpected MATLAB expression.
function used is as follows
function [ x, ex ] = newton( f, df, x0, tol, nmax )
%



% NEWTON Newton's Method
%   Newton's method for finding successively better approximations to the 
%   zeroes of a real-valued function.
%
% Input:
%   f - input funtion
%   df - derived input function
%   x0 - inicial aproximation
%   tol - tolerance
%   nmax - maximum number of iterations
%
% Output:
%   x - aproximation to root
%   ex - error estimate
%
% Example:
%  [ x, ex ] = newton( 'exp(x)+x', 'exp(x)+1', 0, 0.5*10^-5, 10 )
      if nargin == 3
          tol = 1e-4;
          nmax = 1e1;
      elseif nargin == 4
          nmax = 1e1;
      elseif nargin ~= 5
          error('newton: invalid input parameters');
      end
      f = inline(f);
      df = inline(df);
      x(1) = x0 - (f(x0)/df(x0));
      ex(1) = abs(x(1)-x0);
      k = 2;
      while (ex(k-1) >= tol) && (k <= nmax)
          x(k) = x(k-1) - (f(x(k-1))/df(x(k-1)));
          ex(k) = abs(x(k)-x(k-1));
          k = k+1;
      end
end

Best Answer

You are missing a multiplication operator:
Try
 newton(x^3-x,3 * x^2-1,-1,1e-5,20) 
                ^ 
             inserted
Edit: I just noticed, that the function header of newton obviously expects strings ast input arguments. Like in the example given:
[ x, ex ] = newton( 'exp(x)+x', 'exp(x)+1', 0, 0.5*10^-5, 10 )
You will have to alter your function call accordingly. However, the Matlab error resulted from the missing multiplication operator.
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