Change prepend=0 to accum_feed[0]

[viktorht]

pseudobatch/pseudobatch/data_correction.py

Line 133 in 8a11e15

feed_in_interval = np.diff(accum_feed, prepend=0)

In the line of code above, we calculate the feed_in_interval from the accumulated field at the moment this is the one-step-diff, i.e.
$$
feed : in : interval : i = accumfeed_i - accumfeed_{i-1}
$$

This produces nan at index i = 0. The question of the issue is what value to put in place of that nan.

I think that the correct value is accum_feed[0], because then it says that the first value in the accumulated feed vector, describes the feed during the first interval. Currently, we force this value to zero in the prepend=0. This has worked because all of our examples have accum_feed[0].