## 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} =} ss2sys  (@var{a},@var{b},@var{c}@{,@var{d}, @var{tsam}, @var{n}, @var{nz}, @var{stname}, @var{inname}, @var{outname}, @var{outlist}@})
##  Create system structure from state-space data.   May be continous,
##  discrete, or mixed (sampeled-data)
## 
## @strong{Inputs}
## @table @var
## @item   a, b, c, d
##  usual state space matrices.
## 
##                default: @var{d} = zero matrix
## 
## @item   tsam
##  sampling rate.  Default: @math{tsam = 0} (continuous system)
## 
## @item  n, nz
##  number of continuous, discrete states in the system
## 
##         default:
## @table @var
## @item tsam = 0
## @math{n = @code{rows}(@var{a})}, @math{nz = 0}
## 
## @item tsam > 0
## @math{ n = 0},       @math{nz = @code{rows}(@var{a})}
## 
##         see below for system partitioning
## 
## @end table
## 
## @item  stname
##  list of strings of state signal names
## 
##            default (@var{stname}=[] on input): @code{x_n} for continuous states,
##                     @code{xd_n} for discrete states
## 
## @item inname
##  list of strings of input signal names
## 
##            default (@var{inname} = [] on input): @code{u_n}
## 
## @item outname
##  list of strings of input signal names
## 
##            default (@var{outname} = [] on input): @code{y_n}
## 
## @item   outlist
## 
##  list of indices of outputs y that are sampled
## 
##            default: 
## @table @var
## @item tsam = 0  
## @math{outlist = []}
## @item tsam > 0  
## @math{outlist = 1:@code{rows}(@var{c})}
## @end table
## 
## Unlike states, discrete/continous outputs may appear in any order.
## 
## @strong{Note} @code{sys2ss} returns a vector @var{yd} where
## @var{yd}(@var{outlist}) = 1; all other entries of @var{yd} are 0.
## 
## @end table
## 
## @strong{Outputs}
## @var{outsys} = system data structure
## 
## @strong{System partitioning}
## 
##  Suppose for simplicity that outlist specified
##   that the first several outputs were continuous and the remaining outputs
##   were discrete.  Then the system is partitioned as
## @example
## @group
## x = [ xc ]  (n x 1)
##     [ xd ]  (nz x 1 discrete states)
## a = [ acc acd ]  b = [ bc ]
##     [ adc add ]      [ bd ]
## c = [ ccc ccd ]  d = [ dc ]
##     [ cdc cdd ]      [ dd ]  
## 
##     (cdc = c(outlist,1:n), etc.)
## @end group
## @end example
## with dynamic equations:
## @ifinfo
## @math{  d/dt xc(t)     = acc*xc(t)      + acd*xd(k*tsam) + bc*u(t)}
## 
## @math{  xd((k+1)*tsam) = adc*xc(k*tsam) + add*xd(k*tsam) + bd*u(k*tsam)}
## 
## @math{  yc(t)      = ccc*xc(t)      + ccd*xd(k*tsam) + dc*u(t)}
## 
## @math{  yd(k*tsam) = cdc*xc(k*tsam) + cdd*xd(k*tsam) + dd*u(k*tsam)}
## @end ifinfo
## @iftex
## @tex
## $$\eqalign{
## {d \over dt} x_c(t)  
##   & =   a_{cc} x_c(t)      + a_{cd} x_d(k*t_{sam}) + bc*u(t) \cr
## x_d((k+1)*t_{sam}) 
##   & =   a_{dc} x_c(k t_{sam}) + a_{dd} x_d(k t_{sam}) + b_d u(k t_{sam}) \cr
## y_c(t)
##  & =  c_{cc} x_c(t) + c_{cd} x_d(k t_{sam}) + d_c u(t) \cr
## y_d(k t_{sam}) 
##   & =  c_{dc} x_c(k t_{sam}) + c_{dd} x_d(k t_{sam}) + d_d u(k t_{sam})
## }$$
## @end tex
## @end iftex
## 
## @strong{Signal partitions}
## @example
## @group
##         | continuous      | discrete               |
## ----------------------------------------------------
## states  | stname(1:n,:)   | stname((n+1):(n+nz),:) |
## ----------------------------------------------------
## outputs | outname(cout,:) | outname(outlist,:)     |
## ----------------------------------------------------
## @end group
## @end example
## where @math{cout} is the list of in 1:@code{rows}(@var{p}) 
## that are not contained in outlist. (Discrete/continuous outputs
## may be entered in any order desired by the user.)
## 
## @strong{Example}
## @example
## octave:1> a = [1 2 3; 4 5 6; 7 8 10]; 
## octave:2> b = [0 0 ; 0 1 ; 1 0];
## octave:3> c = eye(3);
## octave:4> sys = ss2sys(a,b,c,[],0,3,0,list("volts","amps","joules"));
## octave:5> sysout(sys);
## Input(s)
##         1: u_1
##         2: u_2
## 
## Output(s):
##         1: y_1
##         2: y_2
##         3: y_3
## 
## state-space form:
## 3 continuous states, 0 discrete states
## State(s):
##         1: volts
##         2: amps
##         3: joules
## 
## A matrix: 3 x 3
##    1   2   3
##    4   5   6
##    7   8  10
## B matrix: 3 x 2
##   0  0
##   0  1
##   1  0
## C matrix: 3 x 3
##   1  0  0
##   0  1  0
##   0  0  1
## D matrix: 3 x 3
##   0  0
##   0  0
##   0  0
## @end example
## Notice that the @var{D} matrix is constructed  by default to the 
## correct dimensions.  Default input and output signals names were assigned
## since none were given.
## 
## @end deftypefn

function  retsys = ss2sys  (a,b,c,d,tsam,n,nz,stname,inname,outname,outlist)

  ## Written by John Ingram (ingraje@eng.auburn.edu)  July 20, 1996

  save_val = implicit_str_to_num_ok;	# save for later
  implicit_str_to_num_ok = 1;

  ## Test for correct number of inputs
  if ((nargin < 3) | (nargin > 11))
    usage("retsys = ss2sys  (a,b,c{,d,tsam,n,nz,stname,inname,outname,outlist})");
  endif

  ## verify A, B, C, D arguments
  ## If D is not specified, set it to a zero matrix of appriate dimension.
  if (nargin == 3)          d = zeros(rows(c) , columns(b));
  elseif (isempty(d))       d = zeros(rows(c) , columns(b));      endif

  ## Check the dimensions
  [na,m,p] = abcddim(a,b,c,d);

  ## If dimensions are wrong, exit function
  if (m == -1)
    error("a(%dx%d), b(%dx%d), c(%dx%d), d(%dx%d); incompatible", ...
      rows(a), columns(a), rows(b), columns(b), rows(c), columns(c), ...
      rows(d), columns(d));
  endif

  ## check for tsam input
  if(nargin < 5) tsam = 0;
  elseif( !( is_sample(tsam) | (tsam == 0) ) )
    error("tsam must be a nonnegative real scalar");
  endif

  ## check for continuous states
  if( (nargin < 6) & (tsam == 0) )               n = na;
  elseif(nargin < 6)                             n = 0;
  elseif((!is_matrix(n)) | isstr(n))
    error("Parameter n is not a numerical value.");
  elseif( (!is_scalar(n)) | (n < 0 ) | (n != round(n)) )
    if(is_scalar(n))     error("illegal value of n=%d,%e",n,n);
    else                 error("illegal value of n=(%dx%d)", ...
			   rows(n), columns(n));		endif
  endif

  ## check for num discrete states
  if( (nargin < 7) & (tsam == 0)) 		nz = 0;
  elseif(nargin < 7)				nz = na - n;
  elseif((!is_matrix(nz)) | isstr(nz))
    error("Parameter nz is not a numerical value.");
  elseif( (!is_scalar(nz)) | (nz < 0 ) | (nz != round(nz)) )
    if(is_scalar(nz))
      error(["illegal value of nz=",num2str(nz)]);
    else
      error(["illegal value of nz=(",num2str(rows(nz)),"x", ...
	num2str(columns(nz)),")"]);
    endif
  endif

  ## check for total number of states
  if( (n + nz) != na )
    error(["Illegal: a is ",num2str(na),"x",num2str(na),", n=", ...
	num2str(n),", nz=",num2str(nz)]);
  endif

  ## construct system with default names
  retsys.a = a;
  retsys.b = b; 
  retsys.c = c; 
  retsys.d = d;

  retsys.n = n;
  retsys.nz = nz;
  retsys.tsam = tsam;
  retsys.yd = zeros(1,p);     # default value entered below

  ## Set the system vector:  active = 2(ss), updated = [0 0 1];
  retsys.sys = [2, 0, 0, 1]; 

  retsys.stname = sysdefstname(n,nz);
  retsys.inname = sysdefioname(m,"u");
  retsys.outname = sysdefioname(p,"y");

  ## check for state names
  if(nargin >= 8)
    if(!isempty(stname)) retsys = syssetsignals(retsys,"st",stname); endif
  endif

  ## check for input names
  if(nargin >= 9)
    if(!isempty(inname)) retsys = syssetsignals(retsys,"in",inname); endif
  endif

  ## check for output names
  if(nargin >= 10)
    if(!isempty(outname)) retsys = syssetsignals(retsys,"out",outname); endif
  endif

  ## set up yd
  if(nargin < 11)
    retsys = syssetsignals(retsys,"yd",ones(1,p)*(tsam > 0));
  else
    if(!isempty(outlist)) 
      retsys = syssetsignals(retsys,"yd",ones(size(outlist)),outlist);
    endif
  endif

  implicit_str_to_num_ok = save_val;	## restore value
endfunction