/**
 * Detrended Price Oscillator (DPO).
 * Computes DPO[i] = source[i - shift] - SMA(source, period)[i], where
 * shift = floor(period/2) + 1. Outputs are NaN for indices before the
 * shift or when insufficient data exists.
 * @param source Input series
 * @param period Lookback period (must be > 0)
 * @returns Float64Array of DPO values (NaN where undefined)
 */
export declare function dpo(source: ArrayLike<number>, period: number): Float64Array;