Question about physical residual computation for flow sequences in G-LED

[Eason6666-code]

I have a question regarding the computation of the physical residuals mentioned in the method section.Could you please clarify how the physical residual R(H(st​)) is computed for a segment of a flow field time series? Specifically:
(1) Is the residual computed over individual frames or across multiple time steps?
(2)Are gradients (e.g., divergence or Laplacian) estimated via finite differences, spectral methods, or learned operators?
I am particularly interested in how this residual is formulated and applied to evaluate or guide generated flow sequences.
Thank you in advance for your time and help.