Trin

TRIN (the Arms Index) — the advance/decline ratio divided by the up/down volume ratio. It compares the breadth of a move in issues to the breadth in volume; below one is bullish, above one is bearish.

Quick reference

Item	Value
Family	Market Breadth
Input type	CrossSection — the per-symbol state of the whole universe
Output type	f64 (≥ 0; ~1 is balanced)
Output range	0.. (unbounded above)
Default parameters	none
Warmup period	1
Interpretation	Breadth-vs-volume balance

Formula

ad_ratio     = advancers / max(decliners, 1)
volume_ratio = max(advancing_volume, 1.0) / max(declining_volume, 1.0)
trin         = ad_ratio / volume_ratio

TRIN asks whether volume is concentrated in the issues that are moving. A value near 1.0 means issues and volume are in balance; below 1.0 is bullish (advancing issues are absorbing proportionally more volume); above 1.0 is bearish. To stay finite on degenerate ticks the decliner count is floored to one and both volume sums to 1.0. Stateless per tick and O(universe size). See crates/wickra-core/src/indicators/trin.rs.

Parameters

None. Construct with Trin::new().

Parameter	Type	Default	Source
—	—	—	None.

Inputs / Outputs

Indicator<Input = CrossSection, Output = f64>:

use wickra::{CrossSection, Indicator, Trin};

const _: fn(&mut Trin, CrossSection) -> Option<f64> = <Trin as Indicator>::update;

The bindings pass a tick as four equal-length parallel arrays:

• Python: update(change, volume, new_high, new_low); batch(...) returns a 1-D ndarray.
• Node: update(change, volume, newHigh, newLow); batch returns number[].
• WASM: update(change, volume, newHigh, newLow) only; flag arrays are numeric.

Warmup

warmup_period() == 1; defined from the first tick (tests accessors_and_metadata, balanced_breadth_yields_one).

Edge cases

• Balanced breadth. Equal issue and volume ratios give 1.0 (test balanced_breadth_yields_one).
• Heavy declining volume. Pushes TRIN above one (test heavy_declining_volume_pushes_above_one).
• Zero decliners / volume. Counts and volume sums are floored, so the reading stays finite (test zero_decliners_and_volume_are_floored).
• Reset. reset() returns the indicator to not-ready (test reset_clears_state).
• Invalid / empty universe. Rejected at construction by CrossSection::new.

Examples

Rust

use wickra::{CrossSection, Indicator, Member, Trin};

let mut trin = Trin::new();
// 3 advancers / 1 decliner = 3; adv vol 150 / dec vol 50 = 3; TRIN = 1.0.
let tick = CrossSection::new(
    vec![
        Member::new(1.0, 50.0, false, false),
        Member::new(1.0, 50.0, false, false),
        Member::new(1.0, 50.0, false, false),
        Member::new(-1.0, 50.0, false, false),
    ],
    0,
)?;
assert_eq!(trin.update(tick), Some(1.0));

Python

import wickra as ta

trin = ta.Trin()
print(trin.update([1.0, 1.0, 1.0, -1.0], [50.0] * 4, [False] * 4, [False] * 4))
# 1.0

Node

const { Trin } = require('wickra');

const trin = new Trin();
const flags = [false, false, false, false];
console.log(trin.update([1, 1, 1, -1], [50, 50, 50, 50], flags, flags));
// 1

Streaming

import wickra as ta

trin = ta.Trin()
# balanced -> 1.0
print(trin.update([1.0, 1.0, 1.0, -1.0], [50.0] * 4, [False] * 4, [False] * 4))  # 1.0
# 2 up / 2 down = 1; adv vol 20 / dec vol 80 = 0.25; TRIN = 4.0 (bearish)
print(trin.update([1.0, 1.0, -1.0, -1.0], [10.0, 10.0, 40.0, 40.0], [False] * 4, [False] * 4))  # 4.0

Interpretation

TRIN (TRading INdex) is one of the most watched intraday breadth gauges. Note the inverted scale: low is bullish.

1. Below 1.0. Volume is flowing into advancing issues more than their count alone implies — bullish.
2. Above 1.0. Declining issues are soaking up disproportionate volume — bearish.
3. Extremes. Very high TRIN (e.g. > 2) often marks a selling climax / washout that fades; very low TRIN can mark a buying climax.

Common pitfalls

• Inverted scale. Many newcomers read TRIN backwards — remember low is strong.
• Floored inputs. On degenerate ticks (no decliners, one-sided volume) the floors keep TRIN finite but the value is a boundary artefact, not a clean signal.
• Universe must be stable. Changing membership makes the ratios incomparable.

References

• Arms, R. W. (1989). The Arms Index (TRIN).

See also

• Indicator-AdvanceDeclineRatio — the numerator.
• Indicator-UpDownVolumeRatio — the denominator.
• Indicators-Overview — the full taxonomy.