Why the first term of my loss function is zero?

[thevelvetunderground]

I use the same PDE in other progam too, but it works.By the way, whats the order of the loss? The issue:"What is the output of DeepXDE? How can I visualize the results?" seems closed.

[lululxvi]

Code looks OK. Not sure what happened here.

Here is FAQ https://deepxde.readthedocs.io/en/latest/user/faq.html. I don't understand what is "closed".