calculating firing rate proportional to the membrane potential

[Precola]

/encoding
freq = interp(pot[l][m], [-1.069,2.781], [1,20])
/multi_layer
freq = math.ceil(0.102*pot[l][m] + 52.02)
freq1 = math.ceil(200/freq)

Hi:
I just started learning SNN. I want to know these numbers' meaning and formula that you use to calculate firing rate.