Carl Bender's lectures on very powerful but non-rigorous perturbation theory methods used in theoretical physics: [Part 1][1] [Part 2][2] [Part 3][3] [Part 4][4] [Part 5][5] [Part 6][6] [Part 7][7] [Part 8][8] [Part 9][9] [Part 10][10] [Part 11][11] [Part 12][12] [Part 13][13] [Part 14][14] [Part 15][15] [1]: https://www.youtube.com/watch?v=LYNOGk3ZjFM [2]: https://www.youtube.com/watch?v=tV-xIhP7VU8 [3]: https://www.youtube.com/watch?v=_Sm7SNlNUOI [4]: https://www.youtube.com/watch?v=VvqeJkT3uyo [5]: https://www.youtube.com/watch?v=LMw0NZDM5B4 [6]: https://www.youtube.com/watch?v=nWKYrpKn3-0 [7]: https://www.youtube.com/watch?v=pyEQXMKfEnA [8]: https://www.youtube.com/watch?v=YGDTW7mNUKM [9]: https://www.youtube.com/watch?v=rs2iJugn808 [10]: https://www.youtube.com/watch?v=vem9Ltth_Hg [11]: https://www.youtube.com/watch?v=9OO-gqj3N0c [12]: https://www.youtube.com/watch?v=clpHq5Rs8a4 [13]: https://www.youtube.com/watch?v=ibR4k-HvRm4 [14]: https://www.youtube.com/watch?v=31TegmZpIyc [15]: https://www.youtube.com/watch?v=RqZ0VsEc4F0