dgram

% -*- texinfo -*-
% @deftypefn {Function File} {} dgram (@var{a}, @var{b})
% Return controllability gramian of discrete time system
% @iftex
% @tex
% $$ x_{k+1} = ax_k + bu_k $$
% @end tex
% @end iftex
% @ifinfo
% @example
%   x(k+1) = a x(k) + b u(k)
% @end example
% @end ifinfo
% 
% @strong{Inputs}
% @table @var
% @item a
% @var{n} by @var{n} matrix
% @item b
% @var{n} by @var{m} matrix
% @end table
%
% @strong{Output}
% @table @var
% @item m 
% @var{n} by @var{n} matrix, satisfies
% @iftex
% @tex
% $$ ama^T - m + bb^T = 0 $$
% @end tex
% @end iftex
% @ifinfo
% @example
%  a m a' - m + b*b' = 0
% @end example
% @end ifinfo
% @end table
% @end deftypefn