d2c

% -*- texinfo -*-
% @deftypefn {Function File} {} d2c (@var{sys}, @var{tol})
% @deftypefnx {Function File} {} d2c (@var{sys}, @var{opt})
% Convert a discrete (sub)system into a purely continuous one. 
% The sampling time used is @code{sysgettsam(@var{sys})}.
%
% @strong{Inputs}
% @table @var
% @item   sys
% system data structure with discrete components
% @item   tol
% Scalar value.
% Tolerance for convergence of default @code{'log'} option (see below)
% @item   opt
% conversion option.  Choose from:
% @table @code
% @item         'log'
% (default) Conversion is performed via a matrix logarithm.
% Due to some problems with this computation, it is
% followed by a steepest descent algorithm to identify continuous time
% @var{a}, @var{b}, to get a better fit to the original data.
%
% If called as @code{d2c (@var{sys}, @var{tol})}, with @var{tol}
% positive scalar, the @code{'log'} option is used.  The default value
% for @var{tol} is @code{1e-8}.
% @item        'bi'
% Conversion is performed via bilinear transform
% @math{z = (1 + s T / 2)/(1 - s T / 2)} where @math{T} is the
% system sampling time (see @code{sysgettsam}).
%
% FIXME: bilinear option exits with an error if @var{sys} is not purely
% discrete
% @end table
% @end table
% @strong{Output}
% @table @var
% @item csys 
% continuous time system (same dimensions and signal names as in @var{sys}).
% @end table
% @end deftypefn