% jacobi a func to transform a function f to its jacobian matrix jacomat.
% jacobi works for only function_handle with the format @(x)...
% The input of f should be listed in a column vector separated by semicolon
% The output of jacobi is also an anonymous function.

% For example:
% >> f = @(x) [x(1)^2+x(2)^2; x(1)*x(2)];
% >> Df=jacobi(f)
% >> Df =
%
% function_handle with value:
%
% @(x)[2*x(1),2*x(2);x(2),x(1);]