Calculating the gradient of the measured field for training the PhyLSTM is troublesome since the input signal is very noisy:
Here the gradient is calculated on the field residual, where ripples from the power converter are very visible.
Calculating the derivative of the field with irregularly spaced data and finite difference method is useless since the noise from the original signal causes too much resulting noise on the gradient: 
, and effective filtering cannot be applied due to the irregularly spaced data. Filtering must be applied with full-resolution data, and then adaptively downsampled.