Flag / Pennant

A brief, shallow consolidation against a sharp prior move (the "pole"), resolving in the pole's direction. Bull flag → +1; bear flag → -1.

Quick reference

Item	Value
Family	Chart Patterns
Input type	Candle (uses high, low)
Output type	f64 (+1 / -1 / 0)
Output range	{-1.0, 0.0, +1.0}
Default parameters	none (swing threshold 5%, baked)
Warmup period	4
Interpretation	Continuation in the pole direction

Formula

from the last three pivots pole_start, pole_end, consolidation:
  pole     = |pole_end - pole_start|
  pullback = |consolidation - pole_end|
  qualifies when pullback < 0.5 * pole
  bull flag : pole_end is a swing high → +1
  bear flag : pole_end is a swing low  → -1
otherwise → 0

A flag/pennant is the same structure at this resolution; both are a small counter-move after an impulse. See crates/wickra-core/src/indicators/flag_pennant.rs.

Parameters

None. Swing threshold 0.05 and the 0.5 max-retrace fraction are baked-in constants. FlagPennant::new is infallible.

Inputs / Outputs

const _: fn(&mut wickra::FlagPennant, wickra::Candle) -> Option<f64> =
    <wickra::FlagPennant as wickra::Indicator>::update;

• Python. update((o,h,l,c,v,ts)) → float (never None); batch(open, high, low, close) → 1-D ndarray.
• Node. update(open, high, low, close) → number; batch(open, high, low, close) → number[].
• WASM. update(open, high, low, close) → number.

Warmup

warmup_period() == 4. Three confirmed pivots are required; the earliest bar that can confirm a third pivot is the fourth. Pinned by test accessors_and_metadata.

Edge cases

• Bull flag reports +1 (test bull_flag_is_plus_one).
• Bear flag reports -1 (test bear_flag_is_minus_one).
• Deep pullback (≥ half the pole) reports 0.0 (test deep_pullback_is_not_a_flag).
• reset clears state (test reset_clears_state).
• Streaming equals batch (test batch_equals_streaming).

Examples

Rust

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

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Up-pole 100 → 140 (40), shallow pullback to 130 (10 < 20) → bull flag.
    let bars = [
        (149.85, 150.0, 149.85, 149.85),
        (100.0, 148.5, 100.0, 100.0),
        (101.0, 140.0, 101.0, 101.0),
        (130.0, 138.6, 130.0, 130.0),
        (131.3, 143.0, 131.3, 131.3),
    ];
    let mut pat = FlagPennant::new();
    let mut last = 0.0;
    for (ts, (o, h, l, c)) in bars.iter().enumerate() {
        last = pat.update(Candle::new(*o, *h, *l, *c, 1.0, ts as i64)?).unwrap();
    }
    println!("{last}"); // 1
    Ok(())
}

Python

import wickra as ta

bars = [
    (149.85, 150.0, 149.85, 149.85, 1.0, 0),
    (100.0, 148.5, 100.0, 100.0, 1.0, 1),
    (101.0, 140.0, 101.0, 101.0, 1.0, 2),
    (130.0, 138.6, 130.0, 130.0, 1.0, 3),
    (131.3, 143.0, 131.3, 131.3, 1.0, 4),
]
pat = ta.FlagPennant()
print([pat.update(b) for b in bars][-1])  # 1.0

Node

const wickra = require('wickra');
const bars = [
  [149.85, 150.0, 149.85, 149.85], [100.0, 148.5, 100.0, 100.0],
  [101.0, 140.0, 101.0, 101.0], [130.0, 138.6, 130.0, 130.0],
  [131.3, 143.0, 131.3, 131.3],
];
const pat = new wickra.FlagPennant();
let last = 0;
for (const [o, h, l, c] of bars) last = pat.update(o, h, l, c);
console.log(last); // 1

Streaming

pat = ta.FlagPennant()
for o, h, l, c, v, ts in candle_feed:
    signal = pat.update((o, h, l, c, v, ts))
    if signal > 0:
        pass  # bull flag — continuation higher expected
    elif signal < 0:
        pass  # bear flag — continuation lower expected

Interpretation

1. Continuation bias. The flag confirms on the consolidation pivot and anticipates a breakout in the pole's direction — it is a trend-continuation signal, the opposite intent of the reversal patterns.
2. Pole quality. A larger pole relative to the pullback means a cleaner flag; the half-pole retrace cap keeps deep, range-like pullbacks out.

Common pitfalls

• No volume filter. Classic flags weaken on declining volume; this detector is price-only, so add a volume check for higher-conviction setups.
• Resolution dependence. "Flag" vs "pennant" is a visual distinction this swing-based detector does not separate — both map to the same continuation signal.

See also

• RectangleRange — a deeper, two-sided consolidation.
• Indicators-Overview — full taxonomy.