3.3 KiB
AroonOsc: Aroon Oscillator
Tushar Chande's Aroon system is a dual-line argument. The Oscillator is the verdict.
The Aroon Oscillator condenses the struggle between the "Aroon Up" and "Aroon Down" lines into a single, normalized value. It quantifies not just the existence of a trend, but its freshness. It answers the question: "Are we making new highs faster than we are making new lows?"
The 1995 Standard
Introduced by Tushar Chande in The New Technical Trader (1995), the Aroon system was a departure from price-based momentum. It focused on time. While RSI asks "how much did price move?", Aroon asks "how long has it been since the last extreme?". The Oscillator is simply the arithmetic difference between the two, providing a zero-centered metric for trend bias.
Architecture & Physics
The physics of Aroon are temporal, not spatial. It measures the decay of "recency."
- Time Measurement: We count the bars since the highest high and lowest low within the period.
- Normalization: These counts are converted to a 0-100 scale (100 = happened right now, 0 = happened
Periodbars ago). - Differential: The Oscillator is
Up - Down.
The Drift Resistance
Unlike recursive indicators (EMA, RSI) which accumulate floating-point errors over time, Aroon is stateless in the long term. Its value depends only on the data within the lookback window. This makes it mathematically robust and immune to "poisoning" from bad data in the distant past.
Zero-Allocation Design
The implementation avoids the naive approach of scanning the entire window on every update. Instead, it maintains a circular buffer (RingBuffer) of the last Period + 1 highs and lows.
- Hot Path: The
Updatemethod uses stack-based logic. - Memory: Fixed footprint (two ring buffers of size
Period + 1). - Allocations: Zero heap allocations during streaming updates.
Mathematical Foundation
The math is purely arithmetic.
1. Aroon Up
\text{AroonUp} = \frac{\text{Period} - \text{Days Since High}}{\text{Period}} \times 100
2. Aroon Down
\text{AroonDown} = \frac{\text{Period} - \text{Days Since Low}}{\text{Period}} \times 100
3. The Oscillator
\text{AroonOsc} = \text{AroonUp} - \text{AroonDown}
Performance Profile
The algorithm is O(N) where N is the period, as we must scan the window for extremes. However, for typical periods (14-25), this is negligible.
| Metric | Complexity | Notes |
|---|---|---|
| Throughput | ~10ns / bar | Dependent on Period length |
| Allocations | 0 bytes | Hot path is allocation-free |
| Complexity | O(Period) | Linear scan of the lookback window |
| Precision | double |
Standard floating-point precision |
Validation
We validate against TA-Lib and Tushar Chande's original examples.
- Consistency: Matches TA-Lib outputs exactly.
- Edge Cases: Handles flat markets (where high/low are unchanged) correctly by prioritizing the most recent extreme.
Common Pitfalls
- Lag: Because it looks back
Periodbars, it will not signal a reversal until the previous extreme "ages out" or is superseded. It is a lagging indicator of trend changes. - Flatlining: In strong trends, the oscillator can peg at +100 or -100 for extended periods. This is a feature, not a bug—it indicates a "fresh" extreme on every bar.