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: vl_imgrad.m
    path of file: ./repos/CS_MoCo_LAB/reconstruction/matlab/CS_LAB_matlab/utils/utils_SURF/toolbox/imop
    
    the code of the file until where you have to start completion: function [Fx,Fy] = vl_imgrad(F,varargin) ;
% VL_IMGRAD  Image gradient

    
function [Fx,Fy] = vl_imgrad(F,varargin) ;
% VL_IMGRAD  Image gradient
%   [Fx,Fy] = VL_GRAD(F) returns the finite differencies gradient of the
%   image F. The function uses central differencies and for all but
%   the boundaries pixels, for which it uses forward/backward
%   differencies as appropriate.
%
%   VL_GRAD(F,'forward') uses only forward differencies (except on the
%   lower and right boundaries, where backward difference is used).
%   Similarly, VL_GRAD(F,'backward') uses only backward differencies.
%
%   See also: GRADIENT(), VL_HELP().

% Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
% All rights reserved.
%
% This file is part of the VLFeat library and is made available under
% the terms of the BSD license (see the COPYING file).

type = 'central' ; % forward, backward

for k=1:2:length(varargin)
  switch varargin{k}
    case 'Type'
      type = varargin{k+1} ;
    otherwise
      error(['Parameter ''', varargin{k}, ''' unknown']) ;
  end