Chapter 80: differential equation
DE = differential equation
https://www.youtube.com/watch?v=0kY3Wpvutfs
- guess: ansatz
- energy conservation
- series expansion
- Laplace transform
- Hamiltonian flow
- matrix exponential
- linear operator
80.1 ODE = ordinary DE = ordinary differential equation
https://www.zhihu.com/question/33177784/answer/237992320
https://www.zhihu.com/question/572977895/answer/2814177886
https://zhuanlan.zhihu.com/p/666958247
80.1.1 Sturm-Liouville theory
https://zhuanlan.zhihu.com/p/156941491
https://en.wikipedia.org/wiki/Sturm%E2%80%93Liouville_theory