L-BFGS freezes with 'tensorflow'

[pescap]

Discussed in https://github.com/lululxvi/deepxde/discussions/700

^{Originally posted by pescap May 25, 2022} Hi, https://github.com/lululxvi/deepxde/blob/4cd2178dfc70e06c629c858870a5f64f622982b6/examples/pinn_forward/Poisson_Lshape.py#L25 freezes when using tensorflow as a backend, in CPU and GPU modes.

Example with 5000 ADAM epochs:

'train' took 58.066181 s

Compiling model...
'compile' took 0.019574 s

Training model...

Step      Train loss              Test loss               Test metric
5000      [6.19e-04, 5.82e-04]    [6.10e-04, 5.82e-04]    [] 

and then, nothing.