Define daily change: \( \Delta_t = Close_t - Close_{t-1} \).
\( Gain_t=\max(\Delta_t,0),\ \ Loss_t=\max(-\Delta_t,0) \)
Using Wilder smoothing (EMA-like):
\( AvgGain_t,\ AvgLoss_t \)
\( RS_t = \frac{AvgGain_t}{AvgLoss_t} \)
\( RSI_t = 100 - \frac{100}{1+RS_t} \)