@livefolio/sdk / ema

Function: ema()

ema(series, period): Series

Defined in: features/indicators/ema.ts:48

Computes an Exponential Moving Average (EMA) over a price series.

Math definition:

k   = 2 / (period + 1)          // smoothing factor
EMA[0] = SMA(series[0..period-1])  // seeded from simple average
EMA[i] = series[i] * k + EMA[i-1] * (1 - k)

Warmup: the first period - 1 input bars are consumed to seed the SMA initial value. The first EMA output point corresponds to input index period - 1; subsequent points are computed from the recursive formula. The output array is shorter than the input (no undefined placeholders).

Edge cases:

• period <= 0 — throws Error.
• series.length < period — returns [] (not enough data to seed the EMA).
• series.length === period — returns a single-point Series equal to the simple average of all input values.

Parameters

Parameter	Type	Description
series	Series	Input price series sorted in ascending timestamp order.
period	number	Lookback window in bars. Must be a positive integer. Controls the smoothing factor k = 2 / (period + 1): smaller periods react faster to recent prices.

Returns

Series

A Series of length max(0, series.length - period + 1). Each point's timestamp t is taken from the corresponding input bar.

Example

import { ema } from '@livefolio/sdk';

const prices = [
  { t: new Date('2023-01-02'), v: 100 },
  { t: new Date('2023-01-03'), v: 110 },
  { t: new Date('2023-01-04'), v: 120 },
  { t: new Date('2023-01-05'), v: 130 },
];

const result = ema(prices, 3);
// result.length === 2
// result[0] => { t: new Date('2023-01-04'), v: 110 }  // SMA seed: (100+110+120)/3
// result[1] => { t: new Date('2023-01-05'), v: ~116.7 } // EMA: 130*0.5 + 110*0.5