BreadthThrust

The Breadth Thrust (Zweig) — a simple moving average of the advancing-issues share, advancers / (advancers + decliners). A "thrust" fires when this average surges from oversold to overbought within about ten sessions.

Quick reference

Item	Value
Family	Market Breadth
Input type	CrossSection — the per-symbol state of the whole universe
Output type	f64 (a share in 0..=1)
Output range	0..=1
Default parameters	period = 10 (Zweig's classic window)
Warmup period	period
Interpretation	Breadth thrust / oversold reversal

Formula

share = advancers / max(advancers + decliners, 1)   # per tick
thrust = SMA(share, period)

Zweig's breadth thrust smooths the fraction of participating issues that are advancing over a short window (classically 10). The historic signal: the average climbing from below ~0.40 (washed-out breadth) to above ~0.615 within about ten sessions — a rare, reliable start-of-advance signal. The participating count is floored to one so a tick with no advancing or declining issues contributes 0.0. Backed by an internal Sma, so the window sum is O(1) per tick. See crates/wickra-core/src/indicators/breadth_thrust.rs.

Parameters

Parameter	Type	Default	Source
period	usize	(10)	breadth_thrust.rs — BreadthThrust::new(period)

new(period) returns Err(Error::PeriodZero) if period == 0.

Inputs / Outputs

Indicator<Input = CrossSection, Output = f64>:

use wickra::{BreadthThrust, CrossSection, Indicator};

const _: fn(&mut BreadthThrust, CrossSection) -> Option<f64> =
    <BreadthThrust as Indicator>::update;

The bindings pass a tick as four equal-length parallel arrays; the constructor takes the window length:

• Python: BreadthThrust(period), update(change, volume, new_high, new_low); batch(...) returns a 1-D ndarray with NaN during warmup.
• Node: new BreadthThrust(period), update(change, volume, newHigh, newLow); batch returns number[] with NaN during warmup.
• WASM: new BreadthThrust(period), update(...) only; flag arrays are numeric.

Warmup

warmup_period() == period; the SMA emits None until period ticks have been seen (tests accessors_and_metadata, averages_the_advancing_share). A zero period is rejected (test rejects_zero_period).

Edge cases

• Warmup. Returns None (Python/Node NaN) until the window is full (test averages_the_advancing_share).
• Empty participation. A tick with no advancers or decliners floors to a 0.0 share (test empty_participation_floors_to_zero_share).
• Reset. reset() clears the window and returns the indicator to not-ready (test reset_clears_state).
• Zero period. Rejected at construction (test rejects_zero_period).
• Invalid / empty universe. Rejected by CrossSection::new.

Examples

Rust

use wickra::{BreadthThrust, CrossSection, Indicator, Member};

let mut bt = BreadthThrust::new(2)?;
let up = CrossSection::new(vec![Member::new(1.0, 1.0, false, false)], 0)?;
assert_eq!(bt.update(up.clone()), None); // warming up
assert_eq!(bt.update(up), Some(1.0));    // both ticks 100% advancing

Python

import wickra as ta

bt = ta.BreadthThrust(10)
# share = advancers / (advancers + decliners), smoothed over 10 ticks.
print(bt.update([1.0] * 8 + [-1.0] * 2, [10.0] * 10, [False] * 10, [False] * 10))
# None   (warming up)

Node

const { BreadthThrust } = require('wickra');

const bt = new BreadthThrust(2);
const up = [1, 1, 1, 1, 1, 1, 1, 1, -1, -1]; // 8 up, 2 down -> share 0.8
const flags = new Array(10).fill(false);
const vol = new Array(10).fill(10);
console.log(bt.update(up, vol, flags, flags)); // null (warming up)

Streaming

import wickra as ta

bt = ta.BreadthThrust(2)
flags = [False] * 10
vol = [10.0] * 10
print(bt.update([1.0] * 8 + [-1.0] * 2, vol, flags, flags))  # None  (share 0.8, warmup)
print(bt.update([1.0] * 6 + [-1.0] * 4, vol, flags, flags))  # 0.7   (SMA(2) of [0.8, 0.6])

Interpretation

The breadth thrust catches the rare, explosive starts of major advances.

1. The classic signal. A 10-day average of the advancing share rising from below 0.40 to above 0.615 inside ~10 sessions has historically preceded large, durable rallies.
2. Oversold floor. Readings near the low end mark washed-out breadth — fuel for a thrust.
3. Rarity. True thrusts are uncommon; most of the time the indicator just tracks the smoothed advancing share.

Common pitfalls

• Thresholds are conventions. The 0.40 / 0.615 levels are Zweig's; calibrate to your universe and bar interval.
• Period choice. A longer window smooths more but reacts slower, blunting the "within ten sessions" character of the signal.
• Universe must be stable. Changing membership distorts the share.

References

• Zweig, M. (1986). Winning on Wall Street — the Breadth Thrust indicator.

See also

• Indicator-AdvanceDeclineRatio — the unsmoothed advance/decline reading.
• Indicators-Overview — the full taxonomy.
• Warmup-Periods — verified warmup table.