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: addaxis.m
    path of file: ./repos/hctsa/Toolboxes/OpenTSTOOL/tstoolbox/@signal/private
    
    the code of the file until where you have to start completion: function s = addaxis(s, a)

% signal/addaxis
% Add one new axis to signal object
%
% s = addaxis(s)    		% add default axis

    
function s = addaxis(s, a)

% signal/addaxis
% Add one new axis to signal object
%
% s = addaxis(s)    		% add default axis
% s = addaxis(s, axis)		% add axis given by argument

narginchk(1,2);

if nargin < 2
	s.xaxes{end