<?php
/**
 * Orange Management
 *
 * PHP Version 7.0
 *
 * @category   TBD
 * @package    TBD
 * @author     OMS Development Team <dev@oms.com>
 * @author     Dennis Eichhorn <d.eichhorn@oms.com>
 * @copyright  2013 Dennis Eichhorn
 * @license    OMS License 1.0
 * @version    1.0.0
 * @link       http://orange-management.com
 */
namespace phpOMS\Math\Finance;

use phpOMS\Math\Statistic\Average;

/**
 * Finance class.
 *
 * @category   Log
 * @package    Framework
 * @author     OMS Development Team <dev@oms.com>
 * @author     Dennis Eichhorn <d.eichhorn@oms.com>
 * @license    OMS License 1.0
 * @link       http://orange-management.com
 * @since      1.0.0
 */
class FinanceFormulas
{

    /**
     * Annual Percentage Yield
     *
     * @param \float $r Stated annual interest rate
     * @param \int   $n number of times compounded
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAnnualPercentageYield(\float $r, \int $n) : \float
    {
        return pow(1 + $r / $n, $n) - 1;
    }

    /**
     * Annual Percentage Yield
     *
     * @param \float $apy Annual percentage yield
     * @param \int   $n   Number of times compounded
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getStateAnnualInterestRateOfAPY(\float $apy, \int $n) : \float
    {
        return (pow($apy + 1, 1 / $n) - 1) * $n;
    }

    /**
     * Annuity - Future Value
     *
     * @param \float $P Periodic payment
     * @param \float $r Stated annual interest rate
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValueOfAnnuity(\float $P, \float $r, \int $n) : \float
    {
        return $P * (pow(1 + $r, $n) - 1) / $r;
    }

    /**
     * Annuity - Future Value
     *
     * @param \float $fva Future value annuity
     * @param \float $P   Periodic payment
     * @param \float $r   Stated annual interest rate
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNumberOfPeriodsOfFVA(\float $fva, \float $P, \float $r) : \int
    {
        return (int) round(log($fva / $P * $r + 1) / log(1 + $r));
    }

    /**
     * Future Value
     *
     * @param \float $fva Future value annuity
     * @param \float $r   Stated annual interest rate
     * @param \int   $n   Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodicPaymentOfFVA(\float $fva, \float $r, \int $n) : \float
    {
        return $fva / ((pow(1 + $r, $n) - 1) / $r);
    }


    /**
     * Annuity - Future Value w/ Continuous Compounding
     *
     * @param \float $cf Cach flow
     * @param \float $r  Rate
     * @param \int   $t  Time
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValueOfAnnuityConinuousCompounding(\float $cf, \float $r, \int $t) : \float
    {
        return $cf * (exp($r * $t) - 1) / (exp($r) - 1);
    }

    /**
     * Annuity - Future Value w/ Continuous Compounding
     *
     * @param \float $fvacc Future value annuity continuous compoinding
     * @param \float $r     Rate
     * @param \int   $t     Time
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getCashFlowOfFVACC(\float $fvacc, \float $r, \int $t) : \float
    {
        return $fvacc / ((exp($r * $t) - 1) / (exp($r) - 1));
    }

    /**
     * Annuity - Future Value w/ Continuous Compounding
     *
     * @param \float $fvacc Future value annuity continuous compoinding
     * @param \float $cf    Cach flow
     * @param \float $r     Rate
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getTimeOfFVACC(\float $fvacc, \float $cf, \float $r) : \int
    {
        return (int) round(log($fvacc / $cf * (exp($r) - 1) + 1) / $r);
    }

    /**
     * Annuity - Payment (PV)
     *
     * @param \float $pv Present value
     * @param \float $r  Rate per period
     * @param \int   $n  Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAnnuityPaymentPV(\float $pv, \float $r, \int $n) : \float
    {
        return $r * $pv / (1 - pow(1 + $r, -$n));
    }

    /**
     * Annuity - Payment (PV)
     *
     * @param \float $p  Payment
     * @param \float $pv Present value
     * @param \float $r  Rate per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNumberOfAPPV(\float $p, \float $pv, \float $r) : \int
    {
        return (int) round(-log(-($r * $pv / $p - 1)) / log(1 + $r));
    }

    /**
     * Annuity - Payment (PV)
     *
     * @param \float $p Payment
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueOfAPPV(\float $p, \float $r, \int $n) : \float
    {
        return $p / $r * (1 - pow(1 + $r, -$n));
    }

    /**
     * Annuity - Payment (FV)
     *
     * @param \float $fv Present value
     * @param \float $r  Rate per period
     * @param \int   $n  Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAnnuityPaymentFV(\float $fv, \float $r, \int $n) : \float
    {
        return $r * $fv / (pow(1 + $r, $n) - 1);
    }

    /**
     * Annuity - Payment (FV)
     *
     * @param \float $p  Payment
     * @param \float $fv Present value
     * @param \float $r  Rate per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNumberOfAPFV(\float $p, \float $fv, \float $r) : \int
    {
        return (int) round(log($fv * $r / $p + 1) / log(1 + $r));
    }

    /**
     * Annuity - Payment (FV)
     *
     * @param \float $p Payment
     * @param \float $r Present value
     * @param \int   $n Rate per period
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValueOfAPFV(\float $p, \float $r, \int $n) : \float
    {
        return $p / $r * (pow(1 + $r, $n) - 1);
    }

    /**
     * Annuity - Payment Factor (PV)
     *
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAnnutiyPaymentFactorPV(\float $r, \int $n) : \float
    {
        return $r / (1 - pow(1 + $r, -$n));
    }

    /**
     * Annuity - Payment Factor (PV)
     *
     * @param \float $p Payment factor
     * @param \float $r Rate per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNumberOfAPFPV(\float $p, \float $r) : \int
    {
        return (int) round(-log(-($r / $p - 1)) / log(1 + $r));
    }

    /**
     * Annuity - Present Value
     *
     * @param \float $P Periodic payment
     * @param \float $r Stated annual interest rate
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueOfAnnuity(\float $P, \float $r, \int $n) : \float
    {
        return $P * (1 - pow(1 + $r, -$n)) / $r;
    }

    /**
     * Annuity - Present Value
     *
     * @param \float $pva Future value annuity
     * @param \float $P   Periodic payment
     * @param \float $r   Stated annual interest rate
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNumberOfPeriodsOfPVA(\float $pva, \float $P, \float $r) : \int
    {
        return (int) round(-log(-($pva / $P * $r - 1)) / log(1 + $r));
    }

    /**
     * Annuity - Present Value
     *
     * @param \float $pva Future value annuity
     * @param \float $r   Stated annual interest rate
     * @param \int   $n   Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodicPaymentOfPVA(\float $pva, \float $r, \int $n) : \float
    {
        return $pva / ((1 - pow(1 + $r, -$n)) / $r);
    }

    /**
     * Annuity - PV Factor
     *
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueAnnuityFactor(\float $r, \int $n) : \float
    {
        return (1 - pow(1 + $r, -$n)) / $r;
    }

    /**
     * Annuity - PV Factor
     *
     * @param \float $p Payment factor
     * @param \float $r Rete per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodsOfPVAF(\float $p, \float $r) : \int
    {
        return (int) round(-log(-($p * $r - 1)) / log(1 + $r));
    }

    /**
     * Annuity Due - Present Value
     *
     * @param \float $P Periodic payment
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueOfAnnuityDue(\float $P, \float $r, \int $n) : \float
    {
        return $P + $P * ((1 - pow(1 + $r, -($n - 1))) / $r);
    }

    /**
     * Annuity Due - Present Value
     *
     * Using alternative formula for PV
     *
     * @param \float $PV Present value
     * @param \float $r  Rate per period
     * @param \int   $n  Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodicPaymentOfPVAD(\float $PV, \float $r, \int $n) : \float
    {
        return $PV * $r / (1 - pow(1 + $r, -$n)) * 1 / (1 + $r);
    }

    /**
     * Annuity Due - Present Value
     *
     * @param \float $PV Present value
     * @param \float $P  Periodic payment
     * @param \float $r  Rate per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodsOfPVAD(\float $PV, \float $P, \float $r) : \int
    {
        return (int) round((($PV - $P) / $P * $r - 1) / log(1 + $r) + 1);
    }

    /**
     * Annuity Due - Future Value
     *
     * @param \float $P Periodic payment
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValueOfAnnuityDue(\float $P, \float $r, \int $n) : \float
    {
        return (1 + $r) * $P * (pow(1 + $r, $n) - 1) / $r;
    }

    /**
     * Annuity Due - Future Value
     *
     * @param \float $FV Future value
     * @param \float $r  Rate per period
     * @param \int   $n  Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodicPaymentOfFVAD(\float $FV, \float $r, \int $n) : \float
    {
        return $FV / ((1 + $r) * ((pow(1 + $r, $n) - 1) / $r));
    }

    /**
     * Annuity Due - Future Value
     *
     * @param \float $FV Future value
     * @param \float $P  Periodic payment
     * @param \float $r  Rate per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodsOfFVAD(\float $FV, \float $P, \float $r) : \int
    {
        return (int) round(log($FV / (1 + $r) / $P * $r + 1) / log(1 + $r));
    }

    /**
     * Asset to Sales Ratio
     *
     * @param \float $assets  Assets
     * @param \float $revenue Revenue
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAssetToSalesRatio(\float $assets, \float $revenue) : \float
    {
        return $assets / $revenue;
    }

    /**
     * Asset Turnover Ratio
     *
     * @param \float $assets  Assets
     * @param \float $revenue Revenue
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAssetTurnoverRatio(\float $assets, \float $revenue) : \float
    {
        return $revenue / $assets;
    }

    /**
     * Average Collection Period
     *
     * @param \float $receivables Receivables turnover (use getReceivablesTurnover)
     * @param \int   $period      Period
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getAverageCollectionPeriod(\float $receivables, \int $period = 365) : \float
    {
        return $period / $receivables;
    }

    /**
     * Receivables Turnover
     *
     * @param \float $sales       Sales in period
     * @param \float $receivables Avg. account receivables
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getReceivablesTurnover(\float $sales, \float $receivables) : \float
    {
        return $sales / $receivables;
    }

    /**
     * Compound Interest
     *
     * @param \float $P Principal
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getCompoundInterest(\float $P, \float $r, \int $n) : \float
    {
        return $P * (pow(1 + $r, $n) - 1);
    }

    /**
     * Continuous Compounding
     *
     * @param \float $P Principal
     * @param \float $r Rate per period
     * @param \int   $t Time
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getContinuousCompounding(\float $P, \float $r, \int $t) : \float
    {
        return $P * exp($r * $t);
    }

    /**
     * Current Ratio
     *
     * @param \float $assets      Assets
     * @param \float $liabilities Liabilities
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getCurrentRaio(\float $assets, \float $liabilities) : \float
    {
        return $assets / $liabilities;
    }

    /**
     * Days in Inventory
     *
     * @param \float $inventory Inventory turnover
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDaysInInventory(\float $inventory) : \float
    {
        return 365 / $inventory;
    }

    /**
     * Debt Coverage Ratio
     *
     * @param \float $income  Net operating income
     * @param \float $service Debt service
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDebtCoverageRatio(\float $income, \float $service) : \float
    {
        return $income / $service;
    }

    /**
     * Debt Ratio
     *
     * @param \float $liabilities Total liabilities
     * @param \float $assets      Total assets
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDebtRatio(\float $liabilities, \float $assets) : \float
    {
        return $liabilities / $assets;
    }

    /**
     * Debt to Equity Ratio (D/E)
     *
     * @param \float $liabilities Total liabilities
     * @param \float $equity      Total assets
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDebtToEquityRatio(\float $liabilities, \float $equity) : \float
    {
        return $liabilities / $equity;
    }

    /**
     * Debt to Income Ratio (D/I)
     *
     * @param \float $payments Periodic payments
     * @param \float $income   Periodic income
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDebtToIncomeRatio(\float $payments, \float $income) : \float
    {
        return $payments / $income;
    }

    /**
     * Discounted Payback Period
     *
     * @param \float $CF Periodic cash flow
     * @param \float $O1 Initial Investment (Outflow)
     * @param \float $r  Rate
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDiscountedPaybackPeriod(\float $CF, \float $O1, \float $r) : \float
    {
        return log(1 / (1 - $O1 * $r / $CF)) / log(1 + $r);
    }

    /**
     * Doubling Time
     *
     * @param \float $r Rate of return
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDoublingTime(\float $r) : \float
    {
        return log(2) / log(1 + $r);
    }

    /**
     * Doubling Time - Continuous Compounding
     *
     * @param \float $r Rate of return
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getDoublingTimeContinuousCompounding(\float $r) : \float
    {
        return log(2) / $r;
    }

    /**
     * Equivalent Annual Annuity
     *
     * @param \float $NPV Net present value
     * @param \float $r   Rate per period
     * @param \int   $n   Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getEquivalentAnnualAnnuity(\float $NPV, \float $r, \int $n) : \float
    {
        return $r * $NPV / (1 - pow(1 + $r, -$n));
    }

    /**
     * Equivalent Annual Annuity
     *
     * @param \float $C   Equivalent annuity cash flow
     * @param \float $NPV Net present value
     * @param \float $r   Rate per period
     *
     * @return \int
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPeriodsOfEAA(\float $C, \float $NPV, \float $r) : \int
    {
        return (int) round(log(-$r * $NPV / $C + 1) / log(1 + $r));
    }

    /**
     * Equivalent Annual Annuity
     *
     * @param \float $C Net present value
     * @param \float $r Rate per period
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNetPresentValueOfEAA(\float $C, \float $r, \int $n) : \float
    {
        return $C / $r * (1 - pow(1 + $r, -$n));
    }

    /**
     * Free Cash Flow to Equity (FCFE)
     *
     * @param \float $income    Net income
     * @param \float $depamo    Depreciation & amortisation
     * @param \float $capital   Capital expenses
     * @param \float $wc        Change in working capital
     * @param \float $borrowing Net Borrowing
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFreeCashFlowToEquity(\float $income, \float $depamo, \float $capital, \float $wc, \float $borrowing) : \float
    {
        return $income + $depamo - $capital - $wc + $borrowing;
    }

    /**
     * Free Cash Flow to Firm (FCFF)
     *
     * @param \float $ebit    EBIT
     * @param \float $t       Tax rate
     * @param \float $depamo  Depreciation & amortisation
     * @param \float $capital Capital expenses
     * @param \float $wc      Change in working capital
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFreeCashFlowToFirm(\float $ebit, \float $t, \float $depamo, \float $capital, \float $wc) : \float
    {
        return $ebit * (1 - $t) + $depamo - $capital - $wc;
    }

    /**
     * Future Value
     *
     * @param \float $C Cash flow at period 0
     * @param \float $r Rate of return
     * @param \int   $n Numbers of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValue(\float $C, \float $r, \int $n) : \float
    {
        return $C * pow(1 + $r, $n);
    }

    /**
     * Future Value - Continuous Compounding
     *
     * @param \float $PV Present value
     * @param \float $r  Rate of return
     * @param \int   $t  Time
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValueContinuousCompounding(\float $PV, \float $r, \int $t) : \float
    {
        return $PV * exp($r * $t);
    }

    /**
     * Future Value Factor
     *
     * @param \float $r Rate of return
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getFutureValueFactor(\float $r, \int $n) : \float
    {
        return pow(1 + $r, $n);
    }

    /**
     * Future Value Factor
     *
     * @param array $r Rate of return
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getGeometricMeanReturn(array $r) : \float
    {
        return Average::geometricMean($r) - 1;
    }

    /**
     * Growing Annuity - Future Value
     *
     * @param \float $P First payment
     * @param \float $r Rate of return
     * @param \float $g Growth rate
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getGrowingAnnuityFV(\float $P, \float $r, \float $g, \int $n) : \float
    {
        return $P * (pow(1 + $r, $n) - pow(1 + $g, $n)) / ($r - $g);
    }

    /**
     * Growing Annuity - Payment (PV)
     *
     * @param \float $PV Present value
     * @param \float $r  Rate of return
     * @param \float $g  Growth rate
     * @param \int   $n  Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getGrowingAnnuityPaymentPV(\float $PV, \float $r, \float $g, \int $n) : \float
    {
        return $PV * ($r - $g) / (1 - pow((1 + $g) / (1 + $r), $n));
    }

    /**
     * Growing Annuity - Payment (FV)
     *
     * @param \float $FV Present value
     * @param \float $r  Rate of return
     * @param \float $g  Growth rate
     * @param \int   $n  Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getGrowingAnnuityPaymentFV(\float $FV, \float $r, \float $g, \int $n) : \float
    {
        return $FV * ($r - $g) / (pow(1 + $r, $n) - pow(1 + $g, $n));
    }

    /**
     * Growing Annuity - Present Value
     *
     * @param \float $P First payment
     * @param \float $r Rate of return
     * @param \float $g Growth rate
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getGrowingAnnuityPV(\float $P, \float $r, \float $g, \int $n) : \float
    {
        return $P / ($r - $g) * (1 - pow((1 + $g) / (1 + $r), $n));
    }

    /**
     * Growing Perpetuity - Present Value
     *
     * @param \float $D Dividend or coupon at period 1
     * @param \float $r Rate of return
     * @param \float $g Growth rate
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getGrowingPerpetuityPV(\float $D, \float $r, \float $g) : \float
    {
        return $D / ($r - $g);
    }

    /**
     * Interest Coverage Ratio
     *
     * @param \float $ebit    EBIT
     * @param \float $expense Interest expense
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getInterestCoverageRatio(\float $ebit, \float $expense) : \float
    {
        return $ebit / $expense;
    }

    /**
     * Inventory Turnover Ratio
     *
     * @param \float $sales     Sales
     * @param \float $inventory Inventory
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getInventoryTurnoverRatio(\float $sales, \float $inventory) : \float
    {
        return $sales / $inventory;
    }

    /**
     * Net Present Value
     *
     * @param array  $C Cash flow ($C[0] = initial investment)
     * @param \float $r Discount rate
     *
     * @return \float
     *
     * @throws
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNetPresentValue(array $C, \float $r) : \float
    {
        $count = count($C);

        if ($count === 0) {
            throw new \Exception('Dimension');
        }

        $npv = -$C[0];

        for ($i = 1; $i < $count; $i++) {
            $npv += $C[$i] / pow(1 + $r, $i);
        }

        return $npv;
    }

    /**
     * Net Profit Margin
     *
     * @param \float $income Net income
     * @param \float $sales  Sales revenue
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNetProfitMargin(\float $income, \float $sales) : \float
    {
        return $income / $sales;
    }

    /**
     * Net Working Capital
     *
     * @param \float $assets      Current assets
     * @param \float $liabilities Current liabilities
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNetWorkingCapital(\float $assets, \float $liabilities) : \float
    {
        return $assets - $liabilities;
    }

    /**
     * Number of Periods - PV & FV
     *
     * @param \float $FV Future value
     * @param \float $PV Present value
     * @param \float $r  Rate per period
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getNumberOfPeriodsPVFV(\float $FV, \float $PV, \float $r) : \float
    {
        return log($FV / $PV) / log(1 + $r);
    }

    /**
     * Payback Period
     *
     * @param \float $investment Initial investment
     * @param \float $cash       Periodic cash flow
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPaybackPeriod(\float $investment, \float $cash) : \float
    {
        return $investment / $cash;
    }

    /**
     * Perpetuity
     *
     * @param \float $D Dividend or coupon per period
     * @param \float $r Discount rate
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueOfPerpetuity(\float $D, \float $r) : \float
    {
        return $D / $r;
    }

    /**
     * Number of Periods - PV & FV
     *
     * @param \float $C Cash flow at period 1
     * @param \float $r Rate of return
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValue(\float $C, \float $r, \int $n) : \float
    {
        return $C / pow(1 + $r, $n);
    }

    /**
     * PV - Continuous Compounding
     *
     * @param \float $C Cash flow
     * @param \float $r Rate of return
     * @param \int   $t Time
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueContinuousCompounding(\float $C, \float $r, \int $t) : \float
    {
        return $C / exp($r * $t);
    }

    /**
     * Present Value Factor
     *
     * @param \float $r Rate of return
     * @param \int   $n Number of periods
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getPresentValueFactor(\float $r, \int $n) : \float
    {
        return 1 / pow(1 + $r, $n);
    }

    /**
     * Quick Ratio
     *
     * @param \float $assets      Quick assets (current assets - inventory)
     * @param \float $liabilities Current liabilities
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getQuickRatio(\float $assets, \float $liabilities) : \float
    {
        return $assets / $liabilities;
    }

    /**
     * Rate of Inflation
     *
     * @param \float $oldCPI Consumer price index old
     * @param \float $newCPI Consumer price index new
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getRateOfOnflation(\float $oldCPI, \float $newCPI) : \float
    {
        return $newCPI / $oldCPI - 1;
    }

    /**
     * Real Rate of Return
     *
     * @param \float $nominal   Nominal rate
     * @param \float $inflation Inflation rate
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getRealRateOfReturn(\float $nominal, \float $inflation) : \float
    {
        return (1 + $nominal) / (1 + $inflation) - 1;
    }

    /**
     * Receivables Turnover Ratio
     *
     * @param \float $sales      Sales revenue
     * @param \float $receivable Avg. accounts receivable
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getReceivablesTurnoverRatio(\float $sales, \float $receivable) : \float
    {
        return $sales / $receivable;
    }

    /**
     * Receivables Turnover Ratio
     *
     * @param \float $income    Net income
     * @param \float $dividends Dividends
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getRetentionRatio(\float $income, \float $dividends) : \float
    {
        return ($income - $dividends) / $income;
    }

    /**
     * Return on Assets (ROA)
     *
     * @param \float $income Net income
     * @param \float $assets Avg. total assets
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getReturnOnAssets(\float $income, \float $assets) : \float
    {
        return $income / $assets;
    }

    /**
     * Return on Equity (ROE)
     *
     * @param \float $income Net income
     * @param \float $equity Avg. stockholder's equity
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getReturnOnEquity(\float $income, \float $equity) : \float
    {
        return $income / $equity;
    }

    /**
     * Return on Investment (ROI)
     *
     * @param \float $earnings   Earnings
     * @param \float $investment Initial investment
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getReturnOnInvestment(\float $earnings, \float $investment) : \float
    {
        return $earnings / $investment - 1;
    }

    /**
     * Simple Interest
     *
     * @param \float $P Principal
     * @param \float $r Rate
     * @param \int   $t Time
     *
     * @return \float
     *
     * @since  1.0.0
     * @author Dennis Eichhorn
     */
    public static function getSimpleInterest(\float $P, \float $r, \int $t) : \float
    {
        return $P * $r * $t;
    }

}