You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: fdyn.m
    path of file: ./repos/robotics-toolbox-matlab/@SerialLink
    
    the code of the file until where you have to start completion: %SerialLink.fdyn Integrate forward dynamics
%
% [T,Q,QD] = R.fdyn(TMAX, FTFUN) integrates the dynamics of the robot over
% the time  interval 0 to TMAX and returns vectors of time T (Kx1), joint
% position Q (KxN) and joint velocity QD (KxN).  The initial joint position
% and velocity are zero.
    
function called by FDYN
%
%   XDD = FDYN2(T, X, FLAG, ROBOT, TORQUEFUN)
%
% Called by FDYN to evaluate the robot velocity and acceleration for
% forward dynamics.  T is the current time, X = [Q QD] is the state vector,
% ROBOT is the object being integrated, and TORQUEFUN is the string name of
% the function to compute joint torques and called as
%
%       TAU = TORQUEFUN(ROBOT, T, X, VARARGIN)
%
% if not given zero joint torques are assumed.
%
% The result is XDD = [QD QDD].
function xd = fdyn2(t, x, robot, torqfun, varargin)

    n = robot.n;

    q = x(1:n)';
    qd = x(n+1:2*n)';

    % evaluate the torque function if one is given
    if isa(torqfun, 'function_handle')
        tau = torqfun(robot, t, q, qd, varargin{:});
        tau = tau(:)';
        assert(isreal(tau) && length(tau) == n, 'rtb:fdyn:badretval', 'torque function must return vector with N real elements');
    else
        tau = zeros(1,n);
    end