StarcBands

Stoller Average Range Channel — an SMA(close) centerline with bands sized by ATR. Same skeleton as Keltner Channels but with an SMA midline instead of an EMA of typical price.

Quick reference

Field	Value
Family	Bands & Channels
Input type	Candle (uses high, low, close)
Output type	StarcBandsOutput { upper, middle, lower }
Output range	unbounded; lower ≤ middle ≤ upper
Default parameters	sma_period = 6, atr_period = 15, multiplier = 2.0
Warmup period	max(sma_period, atr_period) (15 for defaults)
Interpretation	Swing levels. A flat SMA midline + wide ATR picks larger swing targets than Keltner's reactive EMA midline.

Formula

middle = SMA(close, sma_period)
upper  = middle + multiplier · ATR(atr_period)
lower  = middle − multiplier · ATR(atr_period)

The SMA-of-close centerline is flatter and less reactive than Keltner's EMA-of-typical-price, which is why Stoller's classic configuration pairs a short SMA (6) with a longer ATR (15) — the midline tracks the swing rather than the trend.

Parameters

Name	Type	Default	Constraint	Source
sma_period	usize	6	>= 1	StarcBands::new (starc_bands.rs:64)
atr_period	usize	15	>= 1	starc_bands.rs:64
multiplier	f64	2.0	finite, > 0	starc_bands.rs:65

A zero period returns [Error::PeriodZero]; a non-finite or non-positive multiplier returns [Error::NonPositiveMultiplier]. StarcBands::classic() returns (6, 15, 2.0). Python defaults come from #[pyo3(signature = (sma_period=6, atr_period=15, multiplier=2.0))]; the Node constructor takes all three arguments explicitly.

Inputs / Outputs

use wickra::{Indicator, StarcBands, Candle, StarcBandsOutput};
// StarcBands: Input = Candle, Output = StarcBandsOutput
const _: fn(&mut StarcBands, Candle) -> Option<StarcBandsOutput> = <StarcBands as Indicator>::update;

• Python streaming. update(candle) returns (upper, middle, lower) or None.
• Python batch. StarcBands.batch(high, low, close) returns an (n, 3)np.ndarray with columns [upper, middle, lower]; warmup rows are NaN.
• Node streaming. update(high, low, close) returns a { upper, middle, lower } object or null.
• Node batch. batch(high, low, close) returns a flat Array<number> of length n * 3.

Warmup

The SMA and ATR sub-indicators are fed unconditionally on every candle so they warm up in parallel, and update emits once both are ready. warmup_period() therefore returns max(sma_period, atr_period) — 15 for the classic configuration. The ATR's Wilder seed (atr_period candles) is the binding constraint when atr_period > sma_period.

Edge cases

• Flat market. A constant-OHLC series drives ATR to 0, so the bands collapse onto the SMA (test flat_market_collapses_bands).
• Decomposition. STARC equals an independent SMA(close, sma_period) plus ±multiplier · ATR(atr_period) combined bar-for-bar (test matches_independent_sma_and_atr).
• Ordering. upper >= middle >= lower always holds (ATR >= 0).
• Reset. reset() resets both sub-indicators.

Examples

Rust

use wickra::{BatchExt, Candle, Indicator, StarcBands};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let candles: Vec<Candle> = (0..40)
        .map(|i| {
            let base = 100.0 + f64::from(i);
            Candle::new(base, base + 2.0, base - 2.0, base + 1.0, 10.0, i64::from(i)).unwrap()
        })
        .collect();
    let mut s = StarcBands::classic(); // (6, 15, 2.0)
    if let Some(o) = s.batch(&candles).into_iter().flatten().last() {
        println!("upper={:.2} middle={:.2} lower={:.2}", o.upper, o.middle, o.lower);
    }
    Ok(())
}

Python

import numpy as np
import wickra as ta

s = ta.StarcBands(6, 15, 2.0)
high  = np.array([...], dtype=float)
low   = np.array([...], dtype=float)
close = np.array([...], dtype=float)
bands = s.batch(high, low, close)  # shape (n, 3): [upper, middle, lower]

Node

const ta = require('wickra');
const s = new ta.StarcBands(6, 15, 2.0);
const out = s.update(102, 98, 101); // null during warmup, else { upper, middle, lower }

Interpretation

STARC frames swing trading around a deliberately slow midline:

1. Swing targets. Because the SMA(6) midline is flat relative to price action, the ATR(15) bands sit far enough out to mark realistic swing extremes — Stoller used them to pick profit targets, not entries.
2. Trend bias. Price persistently riding the upper band signals an uptrend; a close back through the midline warns the swing is over.

Compare with Keltner: same MA ± k·ATR skeleton, but Keltner's EMA-of-typical-price midline reacts faster, making it the better trend-following envelope while STARC is the better swing-level tool.

Common pitfalls

• Swapping the periods. The classic setup is a short SMA and a long ATR; reversing them produces a reactive midline with a sluggish band and loses the swing-level character.
• Expecting Keltner numbers. STARC and Keltner differ in both the midline (SMA-of-close vs EMA-of-typical-price) and the default periods, so their bands will not line up even at the same multiplier.

References

• Manning Stoller, STARC Bands, originally published in Technical Analysis of Stocks & Commodities. The "ARC" stands for Average Range Channel; the leading "ST" is Stoller's initials.

See also

• Keltner — EMA-of-typical-price centerline + ATR.
• AtrBands — close-anchored (no SMA), pure volatility band.
• BollingerBands — sigma-based instead of ATR-based.