is=isletter2(str,opt)

function is=isletter2(str,opt)

% ISLETTER2 Check capital/small/non letters of a character array
%   For a string STR, ISLETTER2(STR) returns a vector with 1 for 
%   capital letters, -1 for small letters and 0 otherwise.
% 
%   ISLETTER2(STR,'all') returns 1 if all components of STR are letters. 
% 
%   ISLETTER2(STR,'any') returns 1 if any component of STR is a letter.
% 
%   Example:
%
%       str='Matlab R12.1';
% 
%       is_isletter=isletter(str);
%       is_isletter2=isletter2(str);
%       is_isletter2_all=isletter2(str,'all');
%       is_isletter2_any=isletter2(str,'any');
% 
%       is_isletter =
%            1  1  1  1  1  1  0  1  0  0  0  0
% 
%       is_isletter2 =
%            1 -1 -1 -1 -1 -1  0  1  0  0  0  0
% 
%       is_isletter2_all =
%            0
% 
%       is_isletter2_any =
%            1
% 
%   See also ISLETTER.
      
%   Author: Jrme Briot
%   Contact: [e-mail]
%   Creation: Aug 2006
% 
%   Revision: 
%       Nov 2006: help typo corrections and engine modification.
%                 Thanks to Jos for the review.
% 

% Check number of arguments
nargchk(1,2,nargin);

% Check if STR is a character array
if ~ischar(str)

    error('First input argument must be a character array (string)');
    
end

% Code given by Jos
is = isletter(str) ;
is = is - 2*(str==lower(str) & is) ;

% Additional ALL/ANY check
if nargin==2
    
    switch lower(opt)
        
    case 'all'
        
        is=all(is);
        
    case 'any'
        
        is=any(is);
        
    otherwise 
        
        error('Second optional argument must be ''all'' or ''any''')
        
    end
    
end