Deepxde

Areas of improvement

- Bug fix: `Rectangle.random_boundary_points`
- Add Euler beam example

New APIs

- Add metric: `absolute_percentage_error_std`
- Add a general operator BC `OperatorBC`

Areas of improvement

- Bug fixes
- Add error checking
- Add documentation
- Improve output
- Add more examples
- Improve `PDE` and `IDE`

New APIs

- Add API to set `float32` or `float64`

This is a bugfix release, fixing the support of Python 2.

This is the first release of DeepXDE.