Ref closed loop

diff --git a/tex/4-loop.tex b/tex/4-loop.tex
index bba55bc7b6e822f06758b17f863e06c1defd798b..3081421298b047ec02c926b8a098cd4f23e312d3 100644 (file)
--- a/tex/4-loop.tex
+++ b/tex/4-loop.tex
@@ -726,7 +726,7 @@ This is one of the objectives of the Loki project team.
 Studying human behavior is useful for the design of machines for several reasons.
 The first reason is to reproduce the strengths of humans.
 For example, in the previous section, we discussed the fundamental coupling between humans' perception and action.
-Systems called \defwords{closed-loop systems}{closed-loop system}\footurl{https://en.wikipedia.org/wiki/Control_system} also leverage such a mechanism.
+Systems called \defwords{closed-loop systems}{closed-loop system}\footurl{https://en.wikipedia.org/wiki/Control_system} also leverage such a mechanism~\cite{messaoud14}.
 For example, the non-inverting and inverting amplifiers circuit depicted on \reffig{fig:amplifiers} have the output of their operational amplifier connected to one of their input through a resistor.
 As a result, the output voltage is proportional to the input voltage whose value depends on $R_1$ and $R_2$.
 But most importantly, the feedback loop stabilizes the output voltage to the desired value.