Summary
Bias is RTTA's streaming percentage deviation of price from its simple moving
average. It measures how far the current close sits above or below the SMA, as
a percent of that average.
Update API
value = rtta.Bias(window=20, fillna=True).update(close)
The update(...) call consumes one close. With fillna=False, output is NaN
until the SMA window is full (same warmup policy as the nested SMA).
Theory Of Operation
Bias (common in Asian market practice, also called "percentage bias" or "price bias ratio") is a normalized distance from a moving average. Positive values mean price is extended above the mean; negative values mean it is below. Because the denominator is the average itself, Bias is scale-free and comparable across instruments.
RTTA implements Bias as \(100 \times (close - SMA) / SMA\) using a nested SMA.
Recurrence
Let \(c_t\) be close and \(n\) be window (default \(20\)).
When \(S_t = 0\) or is non-finite, the safe-divide path returns 0 / NaN
consistent with RTTA's safe_divide helper.
Implementation Notes
The recurrence is implemented in src/rtta/indicator.cpp in class Bias. The
SMA member is constructed with the same fillna flag as the outer indicator.