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: model_add_def_rule.m
    path of file: ./repos/voc-dpm/model
    
    the code of the file until where you have to start completion: function [m, rule] = model_add_def_rule(m, lhs, rhs, varargin)
% Add a deformation schema (rule) to the model.

    
function [m, rule] = model_add_def_rule(m, lhs, rhs, varargin)
% Add a deformation schema (rule) to the model.
%   [m, rule] = model_add_def_rule(m, lhs, rhs, varargin)
%
%   Deformation schemas have the form
%
%   LHS(\omega) --f(\omega,\delta)--> RHS(\omega+\delta)
%   where f(\omega,\delta) = offset_w * offset_feat 
%                            + loc_w * loc_feat(\omega) 
%                            + def_w * def_feat(\delta)
%
% Return values
%   m         Updated model
%   rule      New rule added to the model
%
% Arguments
%   m         Model to update
%   lhs       Left-hand-side symbol for the rule
%   rhs       Right-hand-side symbol for the rule
%   varargin  (key, value) pairs that can specify the following:
%   key                         value
%   ---                         -----
%   flip                        True or false (default)
%   offset_w                    Offset/bias parameter value
%   offset_blocklabel           model.blocks index
%   def_w                       Deformation parameters values
%   def_blocklabel              model.blocks index
%   loc_w                       Location/scale parameters values
%   loc_blocklabel              model.blocks index
%   detection_window            Detection window size
%   shift_detection_window      Detection window shift
%   mirror_rule                 Rule structure to horizontally mirror

% AUTORIGHTS
% -------------------------------------------------------
% Copyright (C) 2009-2012 Ross Girshick
% 
% This file is part of the voc-releaseX code
% (http://people.cs.uchicago.edu/~rbg/latent/)
% and is available under the terms of an MIT-like license
% provided in COPYING. Please retain this notice and
% COPYING if you use this file (or a portion of it) in
% your project.
% -------------------------------------------------------

valid_opts = {'flip', 'offset_w', 'offset_blocklabel', ...
              'def_w', 'def_blocklabel', ...
              'loc_w', 'loc_blocklabel', 'detection_window', ...
              'shift_detection_window', 'mirror_rule'};
opts = getopts(varargin, valid_opts);

try
  i = length(m.rules{lhs}) + 1;
catch
  i = 1;
  m.rules{lhs} = [];
end