diff --git a/notebooks/PDSIMintegrators.py b/notebooks/PDSIMintegrators.py
index 885afea7f0ce11d12e25dfd1efc92336f85fd545..a4f21364a9c0dd49aaf0f59d5c2ddcd2e861c8cf 100644
--- a/notebooks/PDSIMintegrators.py
+++ b/notebooks/PDSIMintegrators.py
@@ -1,3 +1,8 @@
+"""
+These integrator classes started their life in PDSim (https://pdsim.readthedocs.io/en/latest/) and since have 
+been updated and some additional functionality has been added
+"""
+
 from __future__ import division, print_function
 
 import abc, math