/**
 * Discount Factor (DF) is the factor by which a future cash flow must be multiplied in order to obtain the present value.
 *
 * @see http://en.wikipedia.org/wiki/Discounting#Discount_factor
 * @param rate
 * @param numOfPeriods
 * @returns
 */
export declare function DF(rate: number, numOfPeriods: number): number[];