--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/python/tfvar.py	Fri May 27 14:24:59 2011 +0530
@@ -0,0 +1,21 @@
+#!/usr/bin/python
+# 11.7
+
+# N and D polynomials in z^{-1} form; discrete case
+import scipy as sp
+from l2r import l2r
+from scipy import signal
+from covar_m import covar_m
+
+def tfvar(N,dN,D,dD):
+    N,dN,D,dD = l2r(N,dN,D,dD)
+    N = N/D[0]
+    D = D/D[0]
+    LN, LD = len(N), len(D)
+    D1 = D
+    if LD<LN:
+        D1 = sp.hstack((D, sp.zeros(LN-LD)))
+        dD1 = dD+LN-LD
+    H = signal.lti(N, D1)
+    yvar = covar_m(H,1)
+    return N,dN,D,dD,yvar