ElderImpulse

Alexander Elder's Impulse System — a tri-state momentum gauge combining the slope of an EMA trend filter with the slope of the MACD histogram.

Quick reference

Field	Value
Family	Price Oscillators
Input type	f64 (single close)
Output type	f64 — one of {−1, 0, +1}
Output range	{−1, 0, +1}
Default parameters	ema_period = 13, macd = 12 / 26 / 9
Warmup period	max(ema_period, macd_slow + macd_signal − 1) + 1
Interpretation	+1 green / buy, −1 red / sell, 0 blue / neutral.

Formula

On each bar, after warmup:

ema_rising  = EMA(close, ema_period)_t > EMA(close, ema_period)_{t-1}
hist_rising = MACD.histogram_t        > MACD.histogram_{t-1}

if  ema_rising  and  hist_rising : Impulse = +1
if  ema_falling and  hist_falling: Impulse = −1
otherwise                        : Impulse =  0

The trend filter (EMA) and momentum filter (MACD histogram) are fed on every input so they warm up in parallel. Judging direction needs one extra bar past the slowest branch, since both branches are compared against their own previous value.

Parameters

Name	Type	Default	Constraint	Source
ema_period	usize	13	>= 1	ElderImpulse::new (elder_impulse.rs:49)
macd_fast	usize	12	>= 1, < macd_slow	inner MacdIndicator
macd_slow	usize	26	>= 1, > macd_fast	inner MACD
macd_signal	usize	9	>= 1	inner MACD

ema_period == 0 returns [Error::PeriodZero]; invalid MACD periods are forwarded from [MacdIndicator::new] (e.g. macd_fast >= macd_slow). ElderImpulse::classic() returns (13, 12, 26, 9). Python defaults come from the pyo3 signature; the Node constructor takes all four arguments explicitly.

Inputs / Outputs

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

A single f64 close in, an Option<f64> out that is always one of {−1.0, 0.0, +1.0}. Python maps this to float | None / a float64np.ndarray with NaN warmup; Node to number | null / Array<number>.

Warmup

warmup_period() returns max(ema_period, macd_slow + macd_signal − 1) + 1. The + 1 is the extra bar needed to compare each branch with its previous value. For the classic config that is max(13, 26 + 9 − 1) + 1 = 35. Pinned by warmup_emits_first_value_at_warmup_period ((3, 2, 4, 3) → warmup 7: inputs 1–6 return None, input 7 emits).

Edge cases

• Constant series. Both the EMA and the MACD histogram are flat, so neither is rising nor falling ⇒ Impulse = 0 (test constant_series_yields_neutral).
• Pure uptrend. The EMA rises and the histogram (eventually) rises with it, so the reading is +1 or 0 — never −1 (test pure_uptrend_signals_buy).
• Reset. reset() resets both branches and clears the previous-value state used for the slope comparison.

Examples

Rust

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

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let prices: Vec<f64> = (1..=300).map(f64::from).collect();
    let mut elder = ElderImpulse::classic(); // (13, 12, 26, 9)
    let last = elder.batch(&prices).into_iter().flatten().last().unwrap();
    println!("impulse on a clean uptrend = {last}"); // 1.0 or 0.0, never -1.0
    Ok(())
}

Python

import numpy as np
import wickra as ta

elder = ta.ElderImpulse(13, 12, 26, 9)
out = elder.batch(np.arange(1, 301, dtype=float))  # values in {-1, 0, 1}, NaN warmup

Node

const ta = require('wickra');
const elder = new ta.ElderImpulse(13, 12, 26, 9);
const v = elder.update(101.0); // null during warmup, else -1 | 0 | 1

Interpretation

Elder's system colours each bar by the agreement of trend and momentum:

• Green (+1). Both the EMA trend and the MACD histogram are rising — Elder permits long entries and forbids shorts.
• Red (−1). Both are falling — short entries permitted, longs forbidden.
• Blue (0). They disagree — Elder's rule is to hold existing positions but take no new ones.

The Impulse is a permission filter layered on top of another entry method, not a stand-alone signal: it tells you which direction of trade is allowed this bar, not exactly when to pull the trigger.

Common pitfalls

• Trading the blue bars. A 0 is not a reversal signal — it just means trend and momentum disagree. Elder uses it only to block new entries.
• Expecting it before bar 35. The two-derivative construction (slope of EMA, slope of MACD histogram) makes the warmup one bar longer than the slower of the two sub-indicators.

References

• Alexander Elder, Come Into My Trading Room, Wiley, 2002 — the Impulse System chapter.

See also

• MacdIndicator — the momentum branch.
• Ema — the trend branch.
• Apo — the raw MACD line without the histogram slope.