Trouble using jacobian inside a function

I wrote a function that uses the Newton-Raphson method to solve a system of n equations and n uknowns (n<= 4 at the moment) but for some reason, I started getting an error concerning using the jacobian matlab function inside my function. The error reads:

??? Undefined function or method 'jacobian' for input arguments of type 'double'.

Error in ==> NewtRap at 21
        J = jacobian(f0,v)

My function code is:

    function [ answer ] = NewtRap(  )
  %UNTITLED2 Summary of this function goes here
  %   Detailed explanation goes here

Input %%%

global syms x y z w

fprintf('\n')
disp('  1 ) One Equation ')
disp('  2 ) Two Equations ')
disp('  3 ) Three Equations ')
disp('  4 ) Four Equations ')
method = input('\n Choose the number of Equations that you have: ');
    if method == 1
        f1 = input('Enter your equation.  Use x as the variable:  ');
        x0 = input('Enter x0: ');
        tol = input('Enter the maximum tolerance: ');
        v = [ x ];              %This is used to define the jacobian
        f0 = [f1];            %This is used to define the jacobian
        J = jacobian(f0,v);
        J_inv = inv(J);

          delta_x = -J_inv*f0;

          %While loop
          dx = [];
          xx = [];
          xx(:,1) = x0;
          tol1 = 100;
          i = 1;
          while tol1 > tol
              i = i + 1;
              dx(:,i-1) = subs(delta_x,v,xx(:,i-1));
              xx(:,i) = xx(:,i-1) + dx(:,i-1);
              tol1 = abs(xx(1,i) - xx(1,i-1));
          end

          answer = xx(:,end);

      elseif method == 2

          f1 = input('Enter your equation.  Use x and y as the variables:  ');
          f2 = input('Enter your equation.  Use x  and y as the variables:  ');
          x0 = input('Enter initial values as [x0 ;y0]:  ');
          tol = input('Enter the maximum tolerance: ');
          v = [x y];                  %This is used to define the jacobian
          f0 = [f1;f2];               %This is used to define the jacobian
          J = jacobian(f0,v);
          J_inv = inv(J);

          delta_x = -J_inv*f0;

          %While loop
          dx = [];
          xx = [];
          xx(:,1) = x0;
          tol1 = 100;
          tol2 = 100;
          i = 1;
          while tol1 > tol || tol2 > tol
              i = i + 1;
              dx(:,i-1) = subs(delta_x,v,xx(:,i-1));
              xx(:,i) = xx(:,i-1) + dx(:,i-1);
              tol1 = abs(xx(1,i) - xx(1,i-1));
              tol2 = abs(xx(2,i) - xx(2,i-1));
          end

          answer = xx(:,end);

      elseif method == 3
          f1 = input('Enter your equation.  Use x, y, and z as the variables:  ');
          f2 = input('Enter your equation.  Use x, y, and z as the variables:  ');
          f3 = input('Enter your equation.  Use x, y, and z as the variables:  ');
          x0 = input('Enter initial values as [x0;y0;z0]:  ');
          tol = input('Enter the maximum tolerance: ');

          v = [x y z];              %This is used to define the jacobian
          f0 = [f1;f2;f3];            %This is used to define the jacobian
          J = jacobian(f0,v);
          J_inv = inv(J);

          delta_x = -J_inv*f0;

          %While loop
          dx = [];
          xx = [];
          xx(:,1) = x0;
          tol1 = 100;
          tol2 = 100;
          tol3 = 100;
          i = 1;
          while tol1 > tol || tol2 > tol || tol3 > tol
              i = i + 1;
              dx(:,i-1) = subs(delta_x,v,xx(:,i-1));
              xx(:,i) = xx(:,i-1) + dx(:,i-1);
              tol1 = abs(xx(1,i) - xx(1,i-1));
              tol2 = abs(xx(2,i) - xx(2,i-1));
              tol3 = abs(xx(3,i) - xx(3,i-1));
          end

          answer = xx(:,end);

      elseif method == 4
          f1 = input('Enter your equation.  Use x, y, z, and w as the variables:  ');
          f2 = input('Enter your equation.  Use x, y, z, and w as the variables:  ');
          f3 = input('Enter your equation.  Use x, y, z, and w as the variables:  ');
          f4 = input('Enter your equation.  Use x, y, z, and w as the variables:  ');

          x0 = input('Enter initial values as [x0;y0;z0;w0]:  ');
          tol = input('Enter the maximum tolerance: ');

          v = [x y z w];              %This is used to define the jacobian
          f0 = [f1;f2;f3;f4];            %This is used to define the jacobian
          J = jacobian(f0,v);
          J_inv = inv(J);

          delta_x = -J_inv*f0;

          %While loop
          dx = [];
          xx = [];
          xx(:,1) = x0;
          tol1 = 100;
          tol2 = 100;
          tol3 = 100;
          tol4 = 100;
          i = 1;
          while tol1 > tol || tol2 > tol || tol3 > tol || tol4 > tol
              i = i + 1;
              dx(:,i-1) = subs(delta_x,v,xx(:,i-1));
              xx(:,i) = xx(:,i-1) + dx(:,i-1);
              tol1 = abs(xx(1,i) - xx(1,i-1));
              tol2 = abs(xx(2,i) - xx(2,i-1));
              tol3 = abs(xx(3,i) - xx(3,i-1));
              tol4 = abs(xx(4,i) - xx(4,i-1));
          end

          answer = xx(:,end);

      elseif method ~= 1 || method ~= 2 || method ~= 3 || method ~= 4
          fprintf('This option is not currently available\n');

      end

end

Answer 1

[Walter Roberson]

The function jacobian is part of the symbolic toolbox and applies only to symbolic expressions.

Perhaps you want the gradient() function?

Answer 2

[David Hagan]

Thanks for the help. I ended up just defining the symbols inside each method instead and it works fine!

[omkar jagan]

how did u do that. Can u explain with some small syntax.

[Jan]

@omkar jagan: David is not active in the forum for 5 years now. Most likely he will not see your question or even remember, what he did some years ago. I suggest to open a new thread and ask a specific question about your own problem.