LadderBottom

Five-bar bullish reversal. Three long black candles step the market down like rungs of a ladder, a fourth black candle finally shows an upper shadow (the first sign of buying), and a white candle then gaps up into its body and closes above the fourth bar's high to confirm the turn.

Quick reference

Field	Value
Family	Candlestick Patterns
Input type	Candle
Output type	f64 — +1.0 bullish, 0.0 otherwise (never -1.0)
Output range	{0.0, +1.0}
Default parameters	none — LadderBottom::new()
Warmup period	5 (first four bars return None)
Interpretation	Bottoming reversal after a stepped decline

Formula

bar1, bar2, bar3 black, with consecutively lower opens AND closes
bar4 black with an upper shadow      (high4 > open4)
bar5 white, opens above bar4's body   (open5 > open4)
     and closes above bar4's high       (close5 > high4)

Bullish-only (never −1.0). The fourth candle's upper shadow is the first hint of buying; the white fifth confirms by closing above bar 4's high (Nison; TA-Lib CDLLADDERBOTTOM). See crates/wickra-core/src/indicators/ladder_bottom.rs.

TA-Lib parity. On the TA-Lib reference pattern series the signals are identical to CDLLADDERBOTTOM (+1 here, +100 there). TA-Lib sizes bodies and shadows against 5- or 10-bar rolling averages ("candle settings"), while Wickra sizes them against the pattern's own bars.

Parameters

None. Constructed with LadderBottom::new().

Signed ±1 encoding

Single-direction shape: +1.0 bullish, 0.0 no pattern — one feature-matrix dimension.

Inputs / Outputs

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

• Warmup emits None. The first four bars return None; from the fifth bar on every bar emits Some(1.0) or Some(0.0).
• Node. update(open, high, low, close) → number | null; batch(open, high, low, close) → Array<number> (NaN on warmup).
• Python. update(candle) → float | None; batch(open, high, low, close) → 1-D array.array('d') (nan on warmup, 0.0 on no-match).

Warmup

warmup_period() == 5. The first four bars return None (first_four_bars_return_zero, accessors_and_metadata).

Edge cases

• Fourth bar needs an upper shadow. Without it (the first buying hint) the result is 0.0 (fourth_bar_without_upper_shadow_yields_zero).
• First three must be descending blacks. Otherwise 0.0 (not_three_descending_blacks_yields_zero).
• Fifth bar must close above bar 4's high. A white bar that opens above bar 4's open but closes at or below high4 yields 0.0.
• Reset. reset() clears the four-bar cache (reset_clears_state).

Examples

Rust

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

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut t = LadderBottom::new();
    println!("{:?}", t.update(Candle::new(20.0, 20.1, 17.9, 18.0, 1.0, 0)?)); // black
    println!("{:?}", t.update(Candle::new(18.0, 18.1, 15.9, 16.0, 1.0, 1)?)); // lower black
    println!("{:?}", t.update(Candle::new(16.0, 16.1, 13.9, 14.0, 1.0, 2)?)); // lower black
    println!("{:?}", t.update(Candle::new(14.0, 15.0, 12.4, 12.5, 1.0, 3)?)); // black, upper shadow
    println!("{:?}", t.update(Candle::new(15.0, 17.1, 14.9, 17.0, 1.0, 4)?)); // white, gaps up
    Ok(())
}

Output:

None
None
None
None
Some(1.0)

Three descending blacks, a fourth black with an upper shadow (high 15 > open 14), then a white candle opening above it (15 > 14) and closing above bar 4's high (17 > 15) — a ladder bottom. This matches ladder_bottom_is_plus_one.

Python

import numpy as np
import wickra as ta

o = np.array([20.0, 18.0, 16.0, 14.0, 15.0])
h = np.array([20.1, 18.1, 16.1, 15.0, 17.1])
l = np.array([17.9, 15.9, 13.9, 12.4, 14.9])
c = np.array([18.0, 16.0, 14.0, 12.5, 17.0])

print(ta.LadderBottom().batch(o, h, l, c))  # array('d', [nan, nan, nan, nan, 1.0])

Node

const ta = require('wickra');
const t = new ta.LadderBottom();
t.update(20, 20.1, 17.9, 18);
t.update(18, 18.1, 15.9, 16);
t.update(16, 16.1, 13.9, 14);
t.update(14, 15, 12.4, 12.5);
console.log(t.update(15, 17.1, 14.9, 17)); // 1

Streaming

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

let mut t = LadderBottom::new();
let candle_stream: Vec<wickra::Candle> = Vec::new(); // your live OHLCV candle feed
for bar in candle_stream {
    if t.update(bar) == Some(1.0) { /* stepped decline reversing */ }
}

Interpretation

1. Exhaustion of a staircase decline. Three orderly down-rungs, then the first buying wick, then a confirming white candle — a bullish bottom.
2. Rare. Five-bar reversals print infrequently; treat as a prompt to confirm.
3. Best at support. Strongest at the foot of an extended decline.

Common pitfalls

• Missing the fourth-bar shadow. The upper shadow on bar 4 is the defining early-buying signal; without it this is just a decline.
• Weak confirmation. A white fifth bar that merely closes up, without clearing bar 4's high, does not count.
• No downtrend context. Only meaningful after a decline.

References

• Steve Nison, Japanese Candlestick Charting Techniques (1991).
• TA-Lib CDLLADDERBOTTOM.

See also

• ConcealingBabySwallow — another rare multi-black bottoming pattern.
• RisingThreeMethods — five-bar bullish continuation.
• Indicators-Overview — the full taxonomy.