Thanks a lot for the link you mentioned.
In PDEs, I do not have the target values explicitly. If in regression, x_i is input, and u_i is its related target, I can use
loss = sum((u_i - y_i)^2, i=1,..,N),

where y_i is the output of the network related to x_i.
However, in PDEs, I do not have u_i explicitly, and only I know other information, such as the values of the First- or Second-order partial differential equation. Therefore, I cannot use loss = sum((u_i-y_i)^2, i=1,..,N).
I tried to apply the inverse transform in my PDEs, and I think it worked correctly. I should examine the suggestion mentioned in the link you introduced.
Thanks a lot.