some work; does not work

py/brown/brown.py

@@ -37,7 +37,10 @@ class BrownIterator(object):
 		if(self._i == 1):
 			return self.x, self.y
 
-		self.px, self.py = self._interaction(self.x, self.y, self.px, self.py)
+		delta_px, delta_py = self._interaction(self.x, self.y)
+		self.px += delta_px
+		self.py += delta_py
+		print(self.px)
 		# XXX: We need the (-1)**i to make the problem
 		# symmetric.
 		self.px[np.isnan(self.px)] = self.speed_of_light * (-1)**self._i