Summary
ElderThermometer is RTTA's streaming Elder-style bar-range thermometer. Each
bar reports its high-low range, the ratio of that range to the previous bar's
range, and a binary "hot" flag when the current range exceeds the previous one.
Update API
result = rtta.ElderThermometer(fillna=True).update(high, low)
# result.ratio, result.hot, result.range
If high < low, the implementation swaps them so range is always non-negative.
The first bar seeds previous range; with fillna=True it returns
ratio=1.0, hot=0.0, and the current range; with fillna=False all fields
are NaN on the first bar.
Theory Of Operation
Alexander Elder uses a market "thermometer" concept to compare today's activity range with yesterday's. Expanding ranges ("hot" bars) often accompany trending or news-driven sessions; contracting ranges suggest quieter conditions. RTTA exposes three related outputs so callers can threshold ratio, use the binary hot flag, or chart raw range.
Recurrence
Let \(H_t, L_t\) be high and low (after optional swap so \(H_t \ge L_t\)).
On the first bar, store \(\rho_t\) as previous range and emit the fillna placeholder. For \(t \ge 1\):
Then set \(\rho_{t}\) as the new previous range.
Implementation Notes
The recurrence is implemented in src/rtta/indicator.cpp in
class ElderThermometer. Result fields are ratio, hot, and range.