diff --git a/math/__init__.py b/math/__init__.py
index 1b60624..236e51b 100644
--- a/math/__init__.py
+++ b/math/__init__.py
@@ -1,7 +1,30 @@
-# $Id: __init__.py,v 1.1 2010-01-20 03:11:01 wirawan Exp $
+# $Id: __init__.py,v 1.2 2010-05-28 18:43:59 wirawan Exp $
 #
 # wpylib.math main module
 # Created: 20091204
 # Wirawan Purwanto
 #
 pass
+
+import numpy
+
+ZERO_TOL = 5.0e-16
+
+def ztol(val, tol=None, copy=True):
+  """Rounds down values to zero if they are below tolerance."""
+  if tol == None: tol = ZERO_TOL
+  if "__iter__" not in dir(val):
+    if numpy.abs(val) < tol:
+      return 0
+    else:
+      return val
+  elif isinstance(val, numpy.ndarray):
+    if copy:
+      rslt = val.copy()
+    else:
+      rslt = val
+    numpy.putmask(rslt, numpy.abs(rslt) < tol, [0])
+    return rslt
+  else:
+    raise ValueError, "Unsupported datatype: %s" % str(type(val))
+