new file mode 100644
--- /dev/null
+++ b/scripts/control/abcddim.m
@@ -0,0 +1,55 @@
+function [n, m, p] = abcdchk (a, b, c, d)
+
+# Usage: [n, m, p] = abcdchk (a, b, c, d)
+#
+# Check for compatibility of the dimensions of the matrices defining
+# the linear system (a, b, c, d).
+#
+# returns n = number of system states, 
+#         m = number of system inputs
+#         p = number of system outputs
+#
+# returns n = m = p = -1 if system is not compatible
+
+  if (nargin != 4)
+    error ("abcdchk: illegal number of arguments.  Need four.")
+  endif
+
+  n = -1;
+  m = -1;
+  p = -1;
+
+  [an, am] = size (a);
+  if (an != am)
+    disp ("abcdchk: a is not square");
+    return;
+  endif
+
+  [bn, bm] = size (b);
+  if (bn != am)
+    disp ("abcdchk: a, b are not compatible");
+    return;
+  endif
+
+  [cn, cm] = size (c);
+  if (cm != an)
+    disp ("abcdchk: a, c are not compatible");
+    return;
+  endif
+
+  [dn, dm] = size (d);
+  if (cn != dn)
+    disp ("abcdchk: c, d are not compatible");
+    return;
+  endif
+
+  if (bm != dm)
+    disp ("abcdchk: b, d are not compatible");
+    return;
+  endif
+
+  n = an;
+  m = bm;
+  p = cn;
+
+endfunction

new file mode 100644
--- /dev/null
+++ b/scripts/control/tzero.m
@@ -0,0 +1,44 @@
+function zr = tzero (a, b, c, d, bal)
+
+# Compute the transmission zeros of a, b, c, d.
+#
+# bal = balancing option (see balance); default is "B".
+#
+# Needs to incorporate mvzero algorithm to isolate finite zeros.
+
+  if (nargin == 4)
+    bal = "B";
+  elseif (nargin ~= 5)
+    error("tzero: illegal number of arguments")
+  endif
+
+  [n, m, p] = abcdchk (a, b, c, d);
+
+  if(m != p)
+
+    disp("warning: tzero: number of inputs,outputs differ -- squaring up")
+
+    if (p > m)
+      disp ("  by padding b, d with zeros")
+      b = [b, zeros (n, p-m)];
+      d = [d, zeros (p, p-m)];
+      m = p;
+    else
+      disp ("  by padding c,d with zeros")
+      c = [c; zeros (m-p, n)];
+      d = [d; zeros (m-p, m)];
+      p = m;
+    endif
+
+    disp ("This is a kludge.  Try again with SISO system.")
+
+  endif
+
+  if (n != -1)
+    ab = [-a -b; c d];
+    bb = [eye (n), zeros (n, m); zeros (p, n), zeros (p, m)];
+    [ab, bb] = balance (ab, bb);
+    zr = qzval (ab, bb);
+  endif
+
+endfunction