## Copyright (C) 1996 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. 
 
function [a,b,c,d] = series(a1,b1,c1,d1,a2,b2,c2,d2)
## Forms the series connection of two systems.
##
## Superseded by sysmult.  Do not use this routine!
## used internally in zp2ss
##
## Type of input: Transfer functions
## Command:       [num,den]=series(num1,den1,num2,den2)
## Forms the series representation of the two transfer functions.
##
## Type of input: State space systems
## Command:       [a,b,c,d]=series(a1,b1,c1,d1,a2,b2,c2,d2)
## Forms the series representation of the two state space system arguments.
## The series connected system will have the inputs of system 1 and the 
## outputs of system 2.
##
## Type of input: system data structure
## Command:       syst=series(syst1,syst2)
## Forms the series representation of the two mu system arguments.
## Written by David Clem August 15, 1994

## If two arguments input, take care of mu system case

  warning("series is superseded by sysmult; use sysmult instead.")

  muflag = 0;
  if(nargin == 2)
    temp=b1;
    [a1,b1,c1,d1]=sys2ss(a1);
    [a2,b2,c2,d2]=sys2ss(temp);
    muflag = 1;
  endif

## If four arguments input, put two transfer functions in series

  if(nargin == 4)
    a = conv(a1,c1);	% was conv1
    b = conv(b1,d1);	% was conv1
    c = 0;
    d = 0;

## Find series combination of 2 state space systems

  elseif((nargin == 8)||(muflag == 1))

## check matrix dimensions
  
    [n1,m1,p1] = abcddim(a1,b1,c1,d1);
    [n2,m2,p2] = abcddim(a2,b2,c2,d2);

    if((n1 == -1) || (n2 == -1))
      error("Incorrect matrix dimensions");
    endif

## check to make sure the number of outputs of system1 equals the number
## of inputs of system2

   if(p1 ~= m2)
     error("System 1 output / System 2 input connection sizes do not match");
   endif

## put the two state space systems in series

    a = [a1, zeros(rows(a1),columns(a2));b2*c1, a2];
    b = [b1;b2*d1];
    c = [d2*c1, c2];
    d = [d2*d1];

## take care of mu output

    if(muflag == 1)
      a=ss2sys(a,b,c,d);
      b=c=d=0;
    endif 
  endif

endfunction