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: SaveESN.m
    path of file: ./repos/NNAEC-NeuralNetworkbasedAcousticEchoCancellation
    
    the code of the file until where you have to start completion: function SaveESN(esn,file_name,varargin)

% SAVE_ESN save an Esn structure to disk. It's saved under the name
% file_name. 
%
% inputs: 
% esn - our Esn structure we want to save
% file_name - a string containing the file we want 
% option - string containing further options that will be forwarded to
% the matlab save instruction
%

    
function SaveESN(esn,file_name,varargin)

% SAVE_ESN save an Esn structure to disk. It's saved under the name
% file_name. 
%
% inputs: 
% esn - our Esn structure we want to save
% file_name - a string containing the file we want 
% option - string containing further options that will be forwarded to
% the matlab save instruction
%
% usages: 
% save_esn(our_trained_esn, 'esn_28_apr_2006', '-V6')
% save_esn(our_trained_esn, 'esn_28_apr_2006')

% Created April 30, 2006, D. Popovici
% Copyright: Fraunhofer IAIS 2006 / Patent pending


if length(varargin) > 0
    option = char(varargin{1}) ; 
else
    option = '' ; 
end