Parabolic SAR

Classic trend classic stop-loss wilder

A trend-following indicator used to determine price direction and potential reversals.

Visual Example

Parabolic SAR — 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 Parabolic SAR indicator is a technical analysis tool that a trend-following indicator used to determine price direction and potential reversals.

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 for setting trailing stop losses and identifying trend reversals. Dots below price indicate an uptrend, while dots above price indicate a downtrend.

Developed by J. Welles Wilder, the Parabolic Stop and Reverse (SAR) uses an acceleration factor that increases as the trend persists. This 'parabolic' nature allows the indicator to stay close to price action and provide timely exit signals when a trend exhausts. — StockCharts ChartSchool

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/overlap.rs):

\[ SAR_{t+1} = SAR_t + AF \times (EP - SAR_t) \]

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

Parameters

Parameter	Default	Description
`acceleration`	0.02	Acceleration factor
`maximum`	0.2	Maximum acceleration

Usage Examples

Streaming (Rust)

use quantwave_core::indicators::SAR;
use quantwave_core::traits::Next;

let mut ind = SAR::new(0.02);
for price in &prices {
    let value = ind.next(price);
}

Streaming (Python)

from quantwave import SAR

ind = SAR(0.02)
for price in prices:
    value = ind.next(price)

Polars Batch (Python)

import polars as pl
import quantwave as qw

def apply_parabolic_sar(series: pl.Series) -> pl.Series:
    ind = qw.SAR(0.02)
    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_parabolic_sar, return_dtype=pl.Float64).alias("parabolic_sar")
    )
    .collect()
)

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

Edge Cases & Limitations

Warm-up: first 0.02 bars may return NaN or partial state per implementation.
Parameter sensitivity: smaller periods increase noise; larger periods increase lag.
Sudden gaps or bad ticks can distort rolling windows — consider pre-filtering.
Single-series indicators ignore volume unless otherwise documented.
Validated via proptests against gold-standard vectors where available.
No look-ahead bias; streaming and Polars batch paths are bit-identical.

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://www.investopedia.com/terms/p/parabolicindicator.asp

Implementation: quantwave-core/src/indicators/overlap.rs (SAR / SAR_METADATA). Parity: quantwave-core/tests/gold_standard/sar.json

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