% LOWER LOWER Convert strings to lower case
% 
% Usage
% 
% The lower function converts a string to lower case with
% the syntax
% 
%    y = lower(x)
% 
% where x is a string, in which case all of the upper case
% characters in x (defined as the range 'A'-'Z') are
% converted to lower case.  Alternately, you can call lower
% with a cell array of strings
% 
%    y = lower(c)
% 
% in which case each string in the cell array is converted to lower case.
function y = lower(x)
  if (isstr(x))
    y = lower_string(x);
  elseif (iscellstr(x))
    y = cell(size(x));
    for i=1:numel(x)
      y{i} = lower_string(x{i});
    end
  else
    error('lower expects a string or cell array of strings as an argument');
  end

function y = lower_string(x)
  y = string(x + ('a'-'A')*(x>='A' && x<='Z'));