Decay Min-Max Channel (DECAYCHANNEL) tracks the highest high and lowest low like Donchian, then applies exponential decay toward the midpoint. Fresh extremes snap the bands outward; time compresses them inward. The result: channels that respect recent price action while gradually forgetting stale levels. This implementation uses true half-life mathematics—50% convergence over the period length—ensuring predictable decay behavior across all timeframes.
Traditional Donchian Channels treat all extremes within the lookback window equally. A high from 19 bars ago has the same influence as a high from 1 bar ago. This works for breakout detection but creates artificial support/resistance levels that persist until they mechanically exit the window.
Traders noticed this rigidity. A 20-day high from exactly 20 days ago shouldn't matter as much as one from 5 days ago. Various "adaptive channel" approaches emerged in the 1990s-2000s, but most used arbitrary decay rates or complex volatility weighting.
DECAYCHANNEL takes a simpler approach: pure exponential decay with mathematically defined half-life. The decay constant $\lambda = \ln(2) / \text{period}$ guarantees that bands converge 50% toward the midpoint over exactly one period. After two periods: 75%. After three: 87.5%. No tuning parameters, no volatility lookups—just consistent, predictable decay.
These raw values constrain the decayed bands—the upper band can never exceed the actual highest high, and the lower band can never go below the actual lowest low.
DECAYCHANNEL is a QuanTAlib-specific indicator with no external reference implementations.
## Common Pitfalls
1.**Decay Rate Confusion**: The period parameter controls half-life, not full decay. At period=100, bands are 50% decayed after 100 bars, not fully converged. For near-complete convergence (>95%), allow 4-5× the period.
2.**Constraint Snap-Back**: When the actual highest high drops (because an old extreme exits the Highest window), the upper band can snap downward even mid-decay. This is intentional—decayed bands never exceed actual extremes.
3.**Initialization Period**: DECAYCHANNEL needs `period` bars to establish meaningful extremes before decay becomes relevant. IsHot reflects this warmup requirement.
4.**Timer State Management**: Using `isNew=false` for bar correction requires restoring both the band values and the decay timers. The implementation handles this via state snapshots, but improper use corrupts both.
5.**Midpoint Targeting**: Bands decay toward the channel midpoint, not toward current price. In strong trends, this means the trailing band decays toward a point that may be far from price, creating asymmetric behavior.
6.**Memory Overhead**: Each instance maintains two Highest/Lowest indicators plus decay state. For period=100, budget ~1.6 KB per instance for the internal monotonic deques plus ~64 bytes for state.
7.**Exponential Sensitivity**: Small period values create aggressive decay. At period=10, bands are 50% converged after just 10 bars. For most applications, period≥50 provides more stable channels.
- Murphy, J. J. (1999). *Technical Analysis of the Financial Markets*. New York Institute of Finance.
- Kaufman, P. J. (2013). *Trading Systems and Methods* (5th ed.). John Wiley & Sons.
- Press, W. H., et al. (2007). *Numerical Recipes: The Art of Scientific Computing* (3rd ed.). Cambridge University Press. [Exponential decay mathematics]
