function ker = linear(arg)


if nargin == 0
   
   % this is the default constructor

   ker.dummy = [];
   
   ker = class(ker, 'linear');
   
elseif isa(a, 'linear');
   
   % this is the copy constructor
   
   ker = a;
   
else

   % there are no other constructors
   
   help linear
   
end