Index: fact/tools/pyscripts/pyfact/fir_filter.py
===================================================================
--- fact/tools/pyscripts/pyfact/fir_filter.py	(revision 12982)
+++ fact/tools/pyscripts/pyfact/fir_filter.py	(revision 12983)
@@ -23,22 +23,19 @@
     def __call__(self, data):
         length = max(len(self.a),len(self.b))-1
-        
-        #print data
-        #print data.ndim
-        #print data.shape
-        if ( data.ndim == 1):
-            initial = np.ones(length)
-            initial *= data[0]
-        elif ( data.ndim == 2):
-            initial = np.ones( (data.shape[0], length) )
-            for i in range(data.shape[0]):
-                initial[i,:] *= data[i,0]
+        if length > 0:
+            if ( data.ndim == 1):
+                initial = np.ones(length)
+                initial *= data[0]
+            elif ( data.ndim == 2):
+                initial = np.ones( (data.shape[0], length) )
+                for i in range(data.shape[0]):
+                    initial[i,:] *= data[i,0]
+            else:
+                print 'HELP.'
+                pass
+            
+            filtered, zf = signal.lfilter(self.b, self.a, data, zi=initial)
         else:
-            print 'HELP.'
-            pass
-        
-        #print 'initial:\n' , initial
-        filtered, zf = signal.lfilter(self.b, self.a, data, zi=initial)
-        #filtered= signal.lfilter(self.b, self.a, data)
+            filtered= signal.lfilter(self.b, self.a, data)            
         return filtered
 
@@ -63,5 +60,6 @@
         b = np.ones(length)
         a = np.zeros(length)
-        a[0] = len(b)
+        if length > 0:
+            a[0] = len(b)
         FirFilter.__init__(self, b, a, 'sliding average')
             
@@ -73,8 +71,8 @@
         b = np.zeros(length)
         a = np.zeros(length)
-
-        b[0] = -1. * ratio
-        b[length-1] = 1.
-        a[0] = 1.
+        if length > 0:
+            b[0] = -1. * ratio
+            b[length-1] = 1.
+            a[0] = 1.
         FirFilter.__init__(self, b, a, 'constant fraction discriminator')