Update README.md

README.md

@@ -60,3 +60,10 @@ in the shell before running the program
 - Generate movie with 
 
 `ffmpeg -i wave.%05d.tif -vcodec libx264 wave.mp4`
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+## Some references ##
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+- Discretizing the wave equation: https://hplgit.github.io/fdm-book/doc/pub/wave/pdf/wave-4print.pdf
+- Boundary condition: https://hal.archives-ouvertes.fr/hal-01374183
+- Cloaking device: https://www.sciencedirect.com/science/article/pii/S0165212514001759
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