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Ultimate Strength Index

Ehlers DSP oscillator strength ehlers adaptive momentum

A lag-reduced version of the RSI using UltimateSmoother on smoothed up/down components.

Visual Example

Ultimate Strength Index — annotated preview mapping to core implementation

Synthetic ideal per library logic. Generated 2026-06-25 IST via docs/generate_all_previews.py (reproducible; maps to core Next<T> implementation).

Description

The Ultimate Strength Index indicator is a technical analysis tool that a lag-reduced version of the rsi using ultimatesmoother on smoothed up/down components.

This indicator is primarily used for identifying key market conditions. It provides a robust signal that can be easily integrated into both simple strategies and more complex machine learning feature pipelines. Compared to its alternatives, it offers a distinct balance of responsiveness and stability.

Traders often combine this with other metrics to confirm signals and avoid false positives during sideways market regimes. It remains a standard tool for systematic trading models.

Use to measure the relative strength of the current market move normalized to the dominant cycle amplitude, giving a volatility-adjusted momentum reading.

The Ultimate Strength Index measures directional momentum as a fraction of the total cycle amplitude. By normalizing momentum to the RMS energy of the dominant cycle, it produces a consistent 0-100 reading that is comparable across different instruments and volatility regimes.

QuantWave implements this indicator via the universal Next<T> trait, guaranteeing bit-identical results between Rust streaming, Python streaming, and Polars batch (.ta() / map_batches) surfaces.

Formula / Specification

Implementation (quantwave-core/src/indicators/usi.rs):

[ \text{SU} = \max(0, \text{Close} - \text{Close}{t-1}) ] [ \text{SD} = \max(0, \text{Close}) ] [ \text{USU} = UltimateSmoother(SMA(\text{SU}, 4), Length) ] [ \text{USD} = UltimateSmoother(SMA(\text{SD}, 4), Length) ] [ \text{USI} = \frac{\text{USU} - \text{USD}}{\text{USU} + \text{USD}} ]} - \text{Close

Gold-standard parity vectors: quantwave-core/tests/gold_standard/usi.json.

Parameters

Parameter Default Description
length 14 UltimateSmoother period

Usage Examples

Streaming (Rust)

use quantwave_core::indicators::USI;
use quantwave_core::traits::Next;

let mut ind = USI::new(14);
for price in &prices {
    let value = ind.next(price);
}

Streaming (Python)

from quantwave import USI

ind = USI(14)
for price in prices:
    value = ind.next(price)

Polars Batch (Python)

import polars as pl
import quantwave as qw

def apply_ultimate_strength_index(series: pl.Series) -> pl.Series:
    ind = qw.USI(14)
    return pl.Series([ind.next(float(v)) for v in series.to_list()])

df = (
    pl.read_csv('ohlcv.csv')
    .lazy()
    .with_columns(
        pl.col("close").map_batches(apply_ultimate_strength_index, return_dtype=pl.Float64).alias("ultimate_strength_index")
    )
    .collect()
)

All surfaces are bit-identical via the single Next<T> implementation and proptests.

Edge Cases & Limitations

  • Recursive DSP filters require a warm-up period; first N bars may be unstable or raw-pass-through.
  • Designed for cyclic/mean-reverting regimes; trending markets can produce lag or drift.
  • Parameter period (or equivalent) controls cutoff — too small adds noise, too large adds lag.
  • Prefer chaining with other Ehlers tools (Roofing Filter, SuperSmoother) on noisy inputs.
  • Validated via proptests against gold-standard vectors where available.
  • No look-ahead bias; suitable for live streaming and batch feature pipelines.

Boundary Behavior

Condition Behavior
Warm-up Leading bars return NaN until warmup_bars is satisfied.
period > len When period exceeds series length, output is all NaN.
NaN inputs NaN in input propagates to output (NaN out).
Invalid params Non-positive period or missing required params raise ValueError.
Empty data Empty input returns an empty result series.

Sources & References

Primary Source: https://github.com/lavs9/quantwave/blob/main/references/traderstipsreference/TRADERS%E2%80%99%20TIPS%20-%20NOVEMBER%202024.html

Implementation: quantwave-core/src/indicators/usi.rs (USI / USI_METADATA). Parity: quantwave-core/tests/gold_standard/usi.json

Provenance: Standards bulk upgrade 2026-06-25 IST — see docs/DOCUMENTATION_STANDARDS.md.