## Copyright (C) 1996,1998 Auburn University.  All Rights Reserved
##
## This file is part of Octave. 
##
## Octave is free software; you can redistribute it and/or modify it 
## under the terms of the GNU General Public License as published by the 
## Free Software Foundation; either version 2, or (at your option) any 
## later version. 
## 
## Octave is distributed in the hope that it will be useful, but WITHOUT 
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
## FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License 
## for more details.
## 
## You should have received a copy of the GNU General Public License 
## along with Octave; see the file COPYING.  If not, write to the Free 
## Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111 USA. 

## -*- texinfo -*-
## @deftypefn {Function File } { @var{sys} =} fir2sys ( @var{num}@{, @var{tsam}, @var{inname}, @var{outname} @} )
##  construct a system data structure from FIR description
## 
## @strong{Inputs:}
## @table @var
## @item num
##  vector of coefficients @math{[c_0 c_1 ... c_n]}
## of the SISO FIR transfer function 
## @ifinfo
## 
## C(z) = c0 + c1*z^@{-1@} + c2*z^@{-2@} + ... + znz^@{-n@}
## 
## @end ifinfo
## @iftex
## @tex
## $$C(z) = c0 + c1*z^{-1} + c2*z^{-2} + ... + znz^{-n}$$
## @end tex
## @end iftex
## 
## @item tsam
##    sampling time (default: 1)
## 
## @item inname
## name of input signal;  may be a string or a list with a single entry.
## 
## @item outname
##  name of output signal; may be a string or a list with a single entry.
## @end table
## 
## @strong{Outputs}
##   @var{sys} (system data structure)
## 
## @strong{Example}
## @example
## octave:1> sys = fir2sys([1 -1 2 4],0.342,"A/D input","filter output");
## octave:2> sysout(sys)
## Input(s)
##         1: A/D input
## 
## Output(s):
##         1: filter output (discrete)
## 
## Sampling interval: 0.342
## transfer function form:
## 1*z^3 - 1*z^2 + 2*z^1 + 4
## -------------------------
## 1*z^3 + 0*z^2 + 0*z^1 + 0
## @end example
## @end deftypefn
 
function sys = fir2sys (num, tsam, inname, outname)

  ## Written by R. Bruce Tenison  July 29, 1994
  ## Name changed to TF2SYS July 1995
  ## updated for new system data structure format July 1996
  ## adapted from tf2sys july 1996

  ## Test for the correct number of input arguments
  if (nargin < 1 | nargin > 4)
    usage('sys=fir2sys(num[,tsam,inname,outname])');
  endif

  ## let tf2sys do the argument checking
  den = [1,zeros(1,length(num)-1)];

  ## check sampling interval (if any)
  if(nargin <= 1)               tsam = 1;		# default 
  elseif (isempty(tsam))        tsam = 1;		endif

  ## Set name of input
  if(nargin < 3)  inname = sysdefioname(1,"u");        endif

  ## Set name of output
  if(nargin < 4)  outname = sysdefioname(1,"y"); 	endif

  sys = tf2sys(num,den,tsam,inname,outname);
  
endfunction