From 9657833b115c8a61509295d2296c6f89e81fd219 Mon Sep 17 00:00:00 2001
From: Prefetch
Date: Fri, 28 May 2021 15:27:37 +0200
Subject: Improve citations

---
 content/know/concept/calculus-of-variations/index.pdc | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'content/know/concept/calculus-of-variations')

diff --git a/content/know/concept/calculus-of-variations/index.pdc b/content/know/concept/calculus-of-variations/index.pdc
index 576863c..a8861cb 100644
--- a/content/know/concept/calculus-of-variations/index.pdc
+++ b/content/know/concept/calculus-of-variations/index.pdc
@@ -338,3 +338,6 @@ And then the remaining $N - M$ equations can be solved in the normal unconstrain
 1.  G.B. Arfken, H.J. Weber,
     *Mathematical methods for physicists*, 6th edition, 2005,
     Elsevier.
+2.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
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