Fibonacci Fan

Three trendlines fanning from the start of the most recent swing leg through its 38.2 / 50 / 61.8 % retracement levels at the leg's end bar (measured back from the leg's end, as in FibRetracement), extended to the current bar.

Quick reference

Item	Value
Family	Fibonacci
Input type	Candle (uses high, low)
Output type	FibFanOutput (fan_382, fan_500, fan_618)
Output range	diverges from the swing start over time
Default parameters	none (swing threshold 5%, baked)
Warmup period	2 (two confirmed pivots)
Interpretation	Sloped, time-aware support/resistance

Formula

last two pivots define a leg start -> end at bars (start_bar, end_bar):
  progress = (cur - start_bar) / (end_bar - start_bar)
  fan(r)   = start + (1 − r) * (end - start) * progress
for r in {0.382, 0.5, 0.618}, cur = current bar index

All three lines emanate from (start_bar, start) and pass through the retracement levels located at end_bar. The retracement is measured back from the end of the leg — the same convention as FibRetracement — so at the end bar the r line sits at end − r·(end − start): fan_382 is the shallowest retracement (closest to the leg's end) and fan_618 the deepest (closest to the start). As cur advances past the end bar the fan opens. Consecutive pivots sit at strictly increasing bars, so the span is never zero. See crates/wickra-core/src/indicators/fib_fan.rs.

Parameters

None. The swing threshold 0.05 is a baked-in family constant; the three fan ratios are fixed. FibFan::new is infallible.

Inputs / Outputs

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

• Python. update((o,h,l,c,v,ts)) → (fan_382, fan_500, fan_618) or None; batch(high, low) → (n, 3) Matrix (NaN warmup).
• Node. update(high, low) → { fan382, fan500, fan618 } or null; batch(high, low) → flat number[] length n*3.
• WASM. update(high, low) → object (same camelCase keys) or null.

Warmup

warmup_period() == 2. Two confirmed pivots define the leg; before that update returns None. Pinned by tests accessors_and_metadata and no_output_before_two_pivots.

Edge cases

• Fan lines open with elapsed time — one bar past the end of a two-bar leg (progress = 1.5) each line sits at start + (1 − r)·(end − start)·1.5, wider than at the end bar (test fan_lines_open_with_elapsed_time).
• reset clears all state (test reset_clears_state).
• Streaming equals batch (test batch_equals_streaming).

Examples

Rust

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

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Leg start 200 (bar 0) -> end 100 (bar 2), confirmed at bar 3.
    let bars = [
        (199.0, 200.0, 199.0, 199.0),
        (160.0, 190.0, 160.0, 160.0), // confirm high @200
        (100.0, 150.0, 100.0, 100.0), // extend low to 100 (bar 2)
        (105.0, 110.0, 105.0, 105.0), // confirm low @100 -> two pivots
    ];
    let mut fan = FibFan::new();
    let mut last = None;
    for (ts, (o, h, l, c)) in bars.iter().enumerate() {
        last = fan.update(Candle::new(*o, *h, *l, *c, 1.0, ts as i64)?);
    }
    let v = last.unwrap();
    // progress = 3 / 2 = 1.5; fan(r) = 200 + (1 − r)·(−100)·1.5.
    println!("{} {} {}", v.fan_382, v.fan_500, v.fan_618); // 107.30000000000001 125 142.7
    Ok(())
}

Python

import wickra as ta

bars = [
    (199.0, 200.0, 199.0, 199.0, 1.0, 0),
    (160.0, 190.0, 160.0, 160.0, 1.0, 1),
    (100.0, 150.0, 100.0, 100.0, 1.0, 2),
    (105.0, 110.0, 105.0, 105.0, 1.0, 3),
]
fan = ta.FibFan()
print([fan.update(b) for b in bars][-1])  # (107.30000000000001, 125.0, 142.7)

Node

const wickra = require('wickra');
const fan = new wickra.FibFan();
const bars = [[200.0, 199.0], [190.0, 160.0], [150.0, 100.0], [110.0, 105.0]];
let last = null;
for (const [h, l] of bars) last = fan.update(h, l);
console.log(last.fan382, last.fan500, last.fan618); // 107.30000000000001 125 142.7

Streaming

fan = ta.FibFan()
for o, h, l, c, v, ts in candle_feed:
    lines = fan.update((o, h, l, c, v, ts))
    if lines is not None and c < lines[2]:
        pass  # price below the 61.8% (deepest) fan line of an up leg — trend weakening

Interpretation

1. Time-aware levels. Unlike a flat retracement grid, fan lines slope, so the "support" price they imply moves with each bar.
2. Trend health. Holding above the fan lines (in an uptrend) signals strength; slicing through them suggests the trend is rolling over.

Common pitfalls

• Diverges without bound. Far past the leg, the fan lines spread widely and lose practical meaning; they are most useful near the swing.
• Latest leg only. Re-anchors when a new leg confirms.
• Label convention. The r line passes through the r retracement measured from the leg's end (end − r·(end − start)), matching FibRetracement. Earlier releases had the fan_382 and fan_618 values swapped; fan_500 is unchanged.

References

• Fischer, R. Fibonacci Applications and Strategies for Traders (1993).

See also

• FibArcs, FibChannel, FibRetracement.
• Indicators-Overview — full taxonomy.