--- a
+++ b/inst/__modred_check_weight__.m
@@ -0,0 +1,49 @@
+## Copyright (C) 2011   Lukas F. Reichlin
+##
+## This file is part of LTI Syncope.
+##
+## LTI Syncope 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 3 of the License, or
+## (at your option) any later version.
+##
+## LTI Syncope 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 LTI Syncope.  If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## check weightings for model reduction commands
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: November 2011
+## Version: 0.1
+
+function [a, b, c, d, job] = __modred_check_weight__ (sys, dt, p = [], m = [])
+
+  sys = ss (sys);  # could be non-lti, therefore ssdata would fail
+
+  if (dt != isdt (sys))
+    error ("modred: ct/dt");  # TODO: error message
+  endif
+
+  [pw, mw] = size (sys);
+  
+  if (! isempty (p) && mw != p)
+    error ("modred: left weight requires %d inputs", p);
+  endif
+  
+  if (! isempty (m) && pw != m)
+    error ("modred: right weight requires %d outputs", m);
+  endif
+
+  [a, b, c, d] = ssdata (sys);
+  
+  job = 1;
+  
+  ## TODO: check system size
+
+endfunction