Market Facilitation Index (MFI BW)

Bill Williams' Market Facilitation Index — how much price movement the market produces per unit of volume. Not the same as the Mfi Money Flow Index; this is the simpler Williams BW-MFI used in his "Trading Chaos" methodology.

Quick reference

Item	Value
Family	Volume
Input type	Candle (uses high, low, volume)
Output type	f64
Output range	[0, ∞)
Default parameters	none
Warmup period	1
Interpretation	Price-move per unit-volume; pair with prior-bar comparison

Formula

MFI_BW_t = (high_t - low_t) / volume_t

A bar with zero volume returns None (no facilitation can be defined). See crates/wickra-core/src/indicators/market_facilitation_index.rs.

Parameters

None.

Inputs / Outputs

Indicator<Input = Candle, Output = f64>. Python: MarketFacilitationIndex().batch(high, low, volume) returns a 1-D np.ndarray with NaN for zero-volume bars. Node: same; update(candle) returns number | null.

Warmup

warmup_period() == 1.

Edge cases

• Zero-volume bar. Returns None.
• Wide-range, low-volume. High MFI — "fake" move per Williams' classification (low participation).
• Reset. Stateless.

Examples

Rust

use wickra::{BatchExt, Candle, Indicator, MarketFacilitationIndex};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let candles: Vec<Candle> = (0..10).map(|i| {
        let b = 100.0 + f64::from(i);
        Candle::new(b, b + 2.0, b - 2.0, b, 1000.0, i as i64).unwrap()
    }).collect();
    let mut m = MarketFacilitationIndex::new();
    println!("row 5 = {:?}", m.batch(&candles)[5]);
    // (h-l)/v = 4/1000 = 0.004
    Ok(())
}

Python

import numpy as np
import wickra as ta

n = 10
base = 100 + np.arange(n, dtype=float)
m = ta.MarketFacilitationIndex()
print(m.batch(base + 2, base - 2, np.full(n, 1000.0)))

Node

const wickra = require('wickra');
const m = new wickra.MarketFacilitationIndex();
// feed h, l, v

Streaming

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

let mut m = MarketFacilitationIndex::new();
let mut prev_mfi: Option<f64> = None;
let mut prev_vol: Option<f64> = None;
let candle_stream: Vec<wickra::Candle> = Vec::new(); // your live OHLCV candle feed
for bar in candle_stream {
    if let Some(v) = m.update(bar) {
        if let (Some(pm), Some(pv)) = (prev_mfi, prev_vol) {
            // Williams' 4-class taxonomy:
            // green (+,+) MFI↑ volume↑: confirmed move
            // fade  (+,-) MFI↑ volume↓: fake move
            // fake  (-,+) MFI↓ volume↑: absorption
            // squat (-,-) MFI↓ volume↓: indecision
        }
        prev_mfi = Some(v);
        prev_vol = Some(bar.volume);
    }
}

Interpretation

Williams' four-class MFI taxonomy (compared to the previous bar):

• Green (MFI ↑, volume ↑). Confirmed move — high participation, large range. Strong continuation.
• Fade (MFI ↑, volume ↓). Fake move — large range on low volume. Likely to retrace.
• Fake (MFI ↓, volume ↑). Absorption — volume up but range down, signals turning point.
• Squat (MFI ↓, volume ↓). Indecision / consolidation.

Pair with Alligator and WilliamsFractals for the full "Trading Chaos" methodology.

Common pitfalls

• Confused with Mfi. Different indicator: this is BW-MFI (range/volume); the other is Money Flow Index (RSI of money flow).
• Absolute level meaningless. MFI depends on instrument's price and volume scale; only the change vs prior bar and comparison with volume change carry signal.

References

• Bill Williams, Trading Chaos (1995) — original BW-MFI and the 4-class taxonomy.

See also

• Mfi — Money Flow Index (different indicator despite name overlap).
• Alligator — Williams' companion.
• WilliamsFractals — Williams' fractal sibling.
• Indicators-Overview — full taxonomy.