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+## 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.
+
+## idxvec = sysidx (sys, sigtype, signamelist)
+## return indices of signals with specified signal names
+## inputs:
+##   sys:         OCST system data structure
+##   sigtype:     signal type to be selected: "in", "out", "st"
+##   signamelist: list of desired signal names
+## outputs:
+##   idxvec: vector of signal indices (appropriate for use with sysprune)
+
+function idxvec = sysidx (sys, sigtype, signamelist)
+
+  if (nargin != 3)
+    usage ("idxvec = sysidx (sys, sigtype, signamelist)");
+  elseif (! is_struct (sys))
+    error ("sys must be a system data structure");
+  elseif (! isstr (sigtype))
+    error ("sigtype must be a string");
+  elseif (rows (sigtype) != 1)
+    [nr, nc] = size (sigtype);
+    error ("sigtype (%d x %d) must be a single string", nr, nc);
+  endif
+
+  ## extract correct set of signal names values
+  [idxvec, msg] = listidx (list ("in", "out", "st", "yd"), sigtype);
+  if (msg)
+    error ("invalid sigtype = %s", sigtype);
+  endif
+
+  syssiglist = sysgetsignals (sys, sigtype);
+  [idxvec, msg] = listidx (syssiglist, signamelist);
+  if (length (msg))
+    error ("sysidx (sigtype = %s): %s", sigtype,
+	   strrep (msg, "strlist", "signamelist"));
+  endif
+
+endfunction