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: dartel3.m
    path of file: ./repos/ExploreASL/External/SPMmodified/toolbox/DARTEL
    
    the code of the file until where you have to start completion: function varargout = dartel3(varargin)
% DARTEL 3D image registration stuff
%
%_______________________________________________________________________
%
% FORMAT v = dartel3(v,g,f,param)
% v     - flow field n1*n2*n3*3 (single precision float)
% g     - first image n1*n2*n3*n4 (single precision float)
% f     - second image n1*n2*n3*n4 (single precision float)
% param - 9 parameters (settings)
%         - [1] Regularisation type, can take values of
%           - 0 Linear elasticity
%           - 1 Membrane energy
%           - 2 Bending energy
%         - [2][3][4] Regularisation parameters
%           - For "membrane energy", the parameters are
%             lambda, unused and id.
%           - For "linear elasticity", the parameters are
%             mu, lambda, and id
%           - For "bending energy", the parameters are
%             lambda, id1 and id2, such that regularisation is by
%             (-lambda*\grad^2 + id1)^2 + id2
%         - [5] Levenberg-Marquardt regularisation
%         - [6] Number of Full Multigrid cycles
%         - [7] Number of relaxation iterations per cycle
%         - [8] K, such that 2^K time points are used to
%               generate the deformations.  A value of zero
%               indicates a small deformation model.
%         - [9] code of 0, 1 or 2.
%               0 - asymmetric sums of squares objective function.
%               1 -  symmetric sums of squares objective function.
%               2 - assumes multinomial distributio
    
function according to a deformation.
% f2 = f1(y)
% f1, f2 and y are single precision floating point.
%
%_______________________________________________________________________
%
% FORMAT v2 = dartel3('resize', v1, dim)
% v1  - input fields n1*n2*n3*n4
% v2  - output field dim1*dim2*dim3*n4
% dim - output dimensions
%
% Resize a field according to dimensions dim.  This is
% a component of the FMG approach.
%
%_______________________________________________________________________
%
% FORMAT v3 = dartel3('brc', v1, v2)
% v1, v2, v3 - flow fields n1*n2*n3*3
%
% Lie Bracket.  Useful for many things
% e.g. Baker-Campbell-Haussdorf series expansion.
% The Lie bracket is denoted by
% v3 = [v1,v2]
% and on scalar fields, is computed by
% v3 = J1*v2 - J2*v1, where J1 and J2 are the Jacobian
% tensor fields. For matrices, the Lie bracket is simply
% [A,B] = A*B-B*A
%
%_______________________________________________________________________
%
% Note that the boundary conditions are circulant throughout.
% Interpolation is trilinear, except for the resize function
% which uses a 2nd degree B-spline (without first deconvolving).
%
%_______________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% John Ashburner
% $Id: dartel3.m 5506 2013-05-14 17:13:43Z john $

%error('Not compiled for %s in MATLAB %s  (see make.m)\n', computer, version);

if nargin==0,
    error('Incorrect usage.');
elseif ~isa(varargin{1},'char'),
    param0 = varargin{4};
    switch param0(1),
    case 1,
        param = [param0(4) param0(2) 0  0 0];
    case 2,
        param = [param0(4) param0(3) param0(2) 0 0];
    otherwise
        param = [param0(4) 0 0 param0(2) param0(3)];
    end