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+# Copyright (C) 1996 A. Scottedward Hodel 
+#
+# 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, 675 Mass Ave, Cambridge, MA 02139, USA. 
+ 
+function  outsys = zp2sys (zer,pol,k,tsam,inname,outname)
+  # sys = zp2sys (zer,pol,k{,tsam,inname,outname})
+  # Create system data structure from zero-pole data
+  # inputs:
+  #   zer: vector of system zeros
+  #   pol: vector of system poles
+  #   k: scalar leading coefficient
+  #   tsam: sampling period. default: 0 (continuous system)
+  #   inname, outname: input/output signal names (strings)
+  # outputs: sys: system data structure
+
+  #  Modified by John Ingram  July 20, 1996  
+  # $Revision: 1.2 $
+
+  save_val = implicit_str_to_num_ok;	# save for restoring later
+  implicit_str_to_num_ok = 1;
+
+  #  Test for the correct number of input arguments
+  if ((nargin < 3) || (nargin > 6))
+    usage("outsys = zp2sys(zer,pol,k[,tsam,inname,outname])");
+  endif
+
+  # check input format 
+  if( ! (is_vector(zer) | isempty(zer) ) )
+    error("zer must be a vector or empty");
+  endif
+  zer = reshape(zer,1,length(zer));		# make it a row vector
+
+  if( ! (is_vector(pol) | isempty(pol)))
+    error("pol must be a vector");
+  endif
+  pol = reshape(pol,1,length(pol));
+
+  if (! is_scalar(k))
+     error('k must be a scalar');
+  endif
+
+  #  Test proper numbers of poles and zeros.  The number of poles must be 
+  #  greater than or equal to the number of zeros.
+  if (length(zer) >  length(pol))
+    error(["number of poles (", num2str(length(pol)), ...
+	") < number of zeros (", num2str(length(zer)),")"]);
+  endif
+
+  #  Set the system transfer function
+  outsys.zer = zer;
+  outsys.pol = pol;
+  outsys.k = k;
+
+  #  Set the system vector:  active = 1, updated = [0 1 0];
+  outsys.sys = [1 0 1 0];
+
+  #  Set defaults
+  outsys.tsam = 0;
+   outsys.n = length(pol);
+  outsys.nz = 0;
+  outsys.yd = 0;	# assume (for now) continuous time outputs
+
+  #  Set the type of system
+  if (nargin > 3)
+    if( !is_scalar(tsam) )
+      error("tsam must be a nonnegative scalar");
+    endif
+    if (tsam < 0)
+      error("sampling time must be positve")
+    elseif (tsam > 0)
+      [outsys.n,outsys.nz] = swap(outsys.n, outsys.nz);
+      outsys.yd = 1;		# discrete-time output
+    endif
+
+    outsys.tsam = tsam;
+  endif
+
+  outsys.inname = sysdefioname(1,"u");
+  outsys.outname = sysdefioname(1,"y");
+  outsys.stname = sysdefstname(outsys.n,outsys.nz);
+
+  #  Set name of input
+  if (nargin > 4)
+    if (rows(inname) > 1)
+      warning("zp2sys: ",num2str(rows(inname))," input names given, 1st used");
+      inname = inname(1,:);
+    endif
+    outsys.inname(1,1:length(inname)) = inname;
+  endif
+
+  #  Set name of output
+  if (nargin > 5)
+    if (rows(outname) > 1)
+      warning("zp2sys: ",num2str(rows(outname)), ...
+	" output names given, 1st used");
+      outname = outname(1,:);  
+    endif
+    outsys.outname(1,1:length(outname)) = outname;  
+  endif 
+
+  implicit_str_to_num_ok = save_val;
+endfunction