diff --git a/examples/structured_1d_dgsem/elixir_linearizedeuler_characteristic_system.jl b/examples/structured_1d_dgsem/elixir_linearizedeuler_characteristic_system.jl
index 29f4bd0a8cf..663b25b18c0 100644
--- a/examples/structured_1d_dgsem/elixir_linearizedeuler_characteristic_system.jl
+++ b/examples/structured_1d_dgsem/elixir_linearizedeuler_characteristic_system.jl
@@ -19,6 +19,8 @@ cells_per_dimension = (64,)
 
 mesh = StructuredMesh(cells_per_dimension, coordinates_min, coordinates_max)
 
+# For eigensystem of the linearized Euler equations see e.g.
+# https://www.nas.nasa.gov/assets/nas/pdf/ams/2018/introtocfd/Intro2CFD_Lecture1_Pulliam_Euler_WaveEQ.pdf
 # Linearized Euler: Eigensystem
 lin_euler_eigvals = [v_0 - c_0; v_0; v_0 + c_0]
 lin_euler_eigvecs = [-rho_0/c_0 1 rho_0/c_0;