/**
 * Exponential Moving Average (EMA).
 * Seeds on the first non-NaN value and uses the standard EMA recurrence.
 * Preserves NaN gaps in the input: outputs are NaN until enough valid samples
 * have been seen to initialize the EMA.
 * @param source Input series
 * @param period Smoothing period (must be > 0)
 * @returns Float64Array of EMA values (NaN where undefined)
 */
export declare function ema(source: ArrayLike<number>, period: number): Float64Array;