function sysc = d2c(sys,method,varargin)
%D2C  Conversion of discrete LTI models to continuous time.
%
%   SYSC = D2C(SYSD,METHOD) produces a continuous-time model SYSC
%   that is equivalent to the discrete-time LTI model SYSD.  
%   The string METHOD selects the conversion method among the 
%   following:
%      'zoh'       Assumes zero-order hold on the inputs.
%      'tustin'    Bilinear (Tustin) approximation.
%      'prewarp'   Tustin approximation with frequency prewarping.  
%                  The critical frequency Wc is specified last as in
%                  D2C(SysD,'prewarp',Wc)
%      'matched'   Matched pole-zero method (for SISO systems only).
%   The default is 'zoh' when METHOD is omitted.
%
%   See also C2D, D2D, LTIMODELS.

%   Clay M. Thompson  7-19-90
%   Revised: P. Gahinet  8-27-96
%   Copyright (c) 1986-98 by The MathWorks, Inc.
%   $Revision: 1.1 $  $Date: 1998/08/26 16:42:31 $

error('D2C is not supported for FRD models.')
