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, 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 + 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; 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) ndarray (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 — at one leg-width past the end the fan has doubled its spread (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.
    println!("{} {} {}", v.fan_382, v.fan_500, v.fan_618); // 142.7 125 107.3
    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])  # (142.7, 125.0, 107.3)

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); // 142.7 125 107.3

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% fan line — 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.

References

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

See also

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