TrendLabel

A discrete {−1, 0, +1} trend state from the sign of the rolling least-squares slope — scale-invariant.

Quick reference

Field	Value
Family	Trend & Directional
Input type	f64
Output type	f64 (one of −1.0, 0.0, +1.0)
Output range	{−1, 0, +1}
Default parameters	period is required (>= 2)
Warmup period	period
Interpretation	+1 rising regression line, −1 falling, 0 perfectly flat.

Formula

slope = Σ (tᵢ − t̄)(xᵢ − x̄) / Σ (tᵢ − t̄)²       (regress price on bar index)
label = +1 if slope > 0,  −1 if slope < 0,  0 if slope == 0

The sign of the regression slope is scale-invariant — it does not depend on the nominal price level — making it a clean, comparable trend state across instruments. The denominator Σ(tᵢ − t̄)² is strictly positive for period >= 2, so the sign is always well-defined. It is the discrete companion to LinRegSlope (which returns the continuous slope).

Source: crates/wickra-core/src/indicators/trend_label.rs.

Parameters

Name	Type	Default	Valid range	Source	Description
period	usize	none	>= 2	trend_label.rs:52	Regression window. < 2 errors with Error::InvalidPeriod.

Inputs / Outputs

From crates/wickra-core/src/indicators/trend_label.rs:

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

Python streams as float | None, batches as a 1-D numpy.ndarray. Node streams as number | null, batches as Array<number>.

Warmup

warmup_period() == period. The unit test accessors_and_metadata pins warmup_period() == 10 for period = 10.

Edge cases

• Rising series. A strictly rising series labels +1; pinned by rising_series_is_plus_one.
• Falling series. A strictly falling series labels −1; pinned by falling_series_is_minus_one.
• Flat series. A constant series labels 0; pinned by flat_series_is_zero.
• Scale invariance. Multiplying the whole series by a constant cannot change the label; pinned by scale_invariant_sign.
• Ternary output. Output is always one of {−1, 0, +1}; pinned by output_is_ternary.

Examples

Rust

use wickra::{BatchExt, Indicator, TrendLabel};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut tl = TrendLabel::new(10)?;
    let prices: Vec<f64> = (0..20).map(f64::from).collect();
    println!("{:?}", tl.batch(&prices).into_iter().flatten().last());
    Ok(())
}

Output:

Some(1.0)

Python

import wickra as ta

tl = ta.TrendLabel(10)
last = None
for i in range(20):
    last = tl.update(float(i))
print(last)

Output:

1.0

Node

const ta = require('wickra');
const tl = new ta.TrendLabel(10);
let last = null;
for (let i = 0; i < 20; i++) last = tl.update(i);
console.log(last);

Output:

1

Interpretation

TrendLabel is the categorical trend filter for feature pipelines and rule engines that want a clean {up, flat, down} state instead of a continuous slope. The sign is scale-invariant, so the same threshold works across instruments. Any magnitude or dead-band tuning ("only count steep trends") should key on the raw LinRegSlope, keeping TrendLabel as the pure sign.

Common pitfalls

• 0 is rare on real data. A perfectly flat regression is unusual; expect almost always ±1. If you want a dead-band around zero, threshold LinRegSlope yourself.

References

Ordinary-least-squares trend estimation; the slope-sign trend label is a common feature-engineering primitive.

See also

• Indicator-LinRegSlope — the continuous slope.
• Indicator-LinRegAngle — slope as an angle.
• Indicators-Overview — the full taxonomy.