--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/python/ch_pol.py	Fri May 27 14:24:59 2011 +0530
@@ -0,0 +1,15 @@
+#!/usr/bin/env python
+
+# function [phi,psi] = ch_pol(N,epsilon)
+# Returns desired characteristic polynomial and numerator
+# N = rise time in number of sample times
+# epsilon = overshoot as a fraction of ss gain
+
+import pylab as pl
+
+def ch_pol(N,epsilon):
+    omega = pl.pi/2/N
+    r = epsilon**(omega/pl.pi)
+    phi = pl.array([1, -2*r*pl.cos(omega), r**2])
+    psi = pl.array([1-r*pl.cos(omega), r**2-r*pl.cos(omega)])
+    return phi, psi