/**
 * Garman-Klass volatility estimator
 * Uses OHLC data, most efficient unbiased estimator
 *
 * Garman, M. B., & Klass, M. J. (1980). "On the Estimation of Security Price Volatilities
 * from Historical Data"
 */
export declare function calculateGarmanKlassVolatility(openPrices: number[], highPrices: number[], lowPrices: number[], closePrices: number[]): number;