BeltHold

Single-bar reversal: a long candle that opens at one extreme of its range (an opening marubozu) and runs the other way — a bullish belt-hold opens at the low and rallies, a bearish one opens at the high and sells off.

Quick reference

Field	Value
Family	Candlestick Patterns
Input type	Candle
Output type	f64 — +1.0 bullish, -1.0 bearish, 0.0 otherwise
Output range	{-1.0, 0.0, +1.0}
Default parameters	shadow_tolerance = 0.05 (5 % of range); bindings use the default
Warmup period	1
Interpretation	Single-bar reversal/continuation from an extreme open

Formula

range = high − low
long body = |close − open| >= 0.5 · range
bullish (+1.0): green, opens at the low   (open − low  <= tol · range) & long body
bearish (-1.0): red,   opens at the high  (high − open <= tol · range) & long body

A belt-hold is exactly an opening marubozu read as a reversal signal: the open sits at the bar extreme (within tol) and the long body runs away from it. See crates/wickra-core/src/indicators/belt_hold.rs.

Parameters

Name	Type	Default	Valid range	Source
shadow_tolerance	f64	0.05	[0.0, 1.0)	BeltHold::with_tolerance (belt_hold.rs)

with_tolerance outside [0, 1) errors (rejects_invalid_tolerance, accepts_valid_tolerance). Python/Node construct with the default.

Signed ±1 encoding

Emits the uniform candlestick sign convention — +1.0 bullish, −1.0 bearish, 0.0 no pattern — a single feature-matrix dimension.

Inputs / Outputs

use wickra::{Indicator, BeltHold, Candle};
// BeltHold: Input = Candle, Output = f64
const _: fn(&mut BeltHold, Candle) -> Option<f64> = <BeltHold as Indicator>::update;

• Always emits a value. Never None; non-matching bars return 0.0.
• Node. update(open, high, low, close) → number; batch(open, high, low, close) → Array<number>.
• Python. update(candle) → float; batch(open, high, low, close) → 1-D numpy.ndarray (0.0 on no-match).

Warmup

warmup_period() == 1 — emits from the first candle (accessors_and_metadata).

Edge cases

• Opening-side shadow. A shadow on the open end disqualifies it (opening_shadow_yields_zero).
• Short body. A body under half the range yields 0.0 (short_body_yields_zero).
• Zero range. A flat bar yields 0.0 (zero_range_yields_zero).
• Reset. reset() clears the has-emitted flag (reset_clears_state).

Examples

Rust

use wickra::{Candle, Indicator, BeltHold};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut t = BeltHold::new();
    // Bullish belt-hold: opens at the low (10), closes near the high.
    println!("{:?}", t.update(Candle::new(10.0, 12.0, 10.0, 11.5, 1.0, 0)?));
    Ok(())
}

Output:

Some(1.0)

The open equals the low and the body is 1.5 of a 2.0 range (≥ 0.5) — a bullish belt-hold. This matches bullish_belt_hold_is_plus_one.

Python

import numpy as np
import wickra as ta

o = np.array([10.0])
h = np.array([12.0])
l = np.array([10.0])
c = np.array([11.5])

print(ta.BeltHold().batch(o, h, l, c))  # [1.]

Node

const ta = require('wickra');
const t = new ta.BeltHold();
console.log(t.update(10, 12, 10, 11.5)); // 1

Streaming

use wickra::{Candle, Indicator, BeltHold};

let mut t = BeltHold::new();
let candle_stream: Vec<wickra::Candle> = Vec::new(); // your live OHLCV candle feed
for bar in candle_stream {
    match t.update(bar) {
        Some(1.0)  => { /* bullish belt-hold — opened at the low and ran */ }
        Some(-1.0) => { /* bearish belt-hold */ }
        _ => {}
    }
}

Interpretation

1. Conviction from the open. Opening at an extreme and running the full body the other way shows one side seized control immediately — read it as a reversal at a turning point or a strong continuation in-trend.
2. Single-bar, so confirm. One bar is weak evidence; pair with location (support/resistance) or a follow-through bar.

Common pitfalls

• It is an opening marubozu. Mechanically identical to OpeningMarubozu; the difference is interpretive (belt-hold names it as a reversal signal).
• No context. A belt-hold mid-range is far weaker than one at an extreme.

References

• Steve Nison, Japanese Candlestick Charting Techniques (1991).

See also

• OpeningMarubozu — the same geometry.
• Marubozu — both ends shaved.
• Indicators-Overview — the full taxonomy.