From bf2497a4bdd133252d6ccae99f76ef5c000d0ebd Mon Sep 17 00:00:00 2001
From: Francesco Massimo
 <francescomassimo@client-172-18-109-92.eduroam.universite-paris-saclay.fr>
Date: Tue, 5 Dec 2023 13:50:50 +0100
Subject: [PATCH] add import libraries in exercise 20

---
 doc/source/exercises.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/doc/source/exercises.rst b/doc/source/exercises.rst
index 013d4b1..a1adb78 100644
--- a/doc/source/exercises.rst
+++ b/doc/source/exercises.rst
@@ -678,8 +678,10 @@ as well as their weight (from which their charge can be computed).
    **Hint 1:** You can extract the energy and charge of each macro-particle of the bunch at the desired ``timestep``, using::
    
       import happi
+      import numpy as np
       import scipy.constants
       import math
+      import matplotlib.pyplot as plt
       
       S=happi.Open()