poi/src/java/org/apache/poi/ss/formula/functions/Mirr.java

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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
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       http://www.apache.org/licenses/LICENSE-2.0

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   distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.poi.ss.formula.functions;

import java.util.Arrays;

import org.apache.poi.ss.formula.eval.ErrorEval;
import org.apache.poi.ss.formula.eval.EvaluationException;

/**
 * Calculates Modified internal rate of return. Syntax is MIRR(cash_flow_values, finance_rate, reinvest_rate)
 *
 * <p>Returns the modified internal rate of return for a series of periodic cash flows. MIRR considers both the cost
 * of the investment and the interest received on reinvestment of cash.</p>
 *
 * Values is an array or a reference to cells that contain numbers. These numbers represent a series of payments (negative values) and income (positive values) occurring at regular periods.
 * <ul>
 *     <li>Values must contain at least one positive value and one negative value to calculate the modified internal rate of return. Otherwise, MIRR returns the #DIV/0! error value.</li>
 *     <li>If an array or reference argument contains text, logical values, or empty cells, those values are ignored; however, cells with the value zero are included.</li>
 * </ul>
 *
 * Finance_rate     is the interest rate you pay on the money used in the cash flows.
 * Reinvest_rate     is the interest rate you receive on the cash flows as you reinvest them.
 *
 * @author Carlos Delgado (carlos dot del dot est at gmail dot com)
 * @author Cedric Walter (cedric dot walter at gmail dot com)
 *
 * @see <a href="http://en.wikipedia.org/wiki/MIRR">Wikipedia on MIRR</a>
 * @see <a href="http://office.microsoft.com/en-001/excel-help/mirr-HP005209180.aspx">Excel MIRR</a>
 * @see Irr
 */
public class Mirr extends MultiOperandNumericFunction {

    public Mirr() {
        super(false, false);
    }

    @Override
    protected int getMaxNumOperands() {
        return 3;
    }

    @Override
    protected double evaluate(double[] values) throws EvaluationException {

        double financeRate = values[values.length-1];
        double reinvestRate = values[values.length-2];

        double[] mirrValues = Arrays.copyOf(values, values.length - 2);

        boolean mirrValuesAreAllNegatives = true;
        for (double mirrValue : mirrValues) {
            mirrValuesAreAllNegatives &= mirrValue < 0;
        }
         if (mirrValuesAreAllNegatives) {
             return -1.0d;
         }

        boolean mirrValuesAreAllPositives = true;
        for (double mirrValue : mirrValues) {
            mirrValuesAreAllPositives &= mirrValue > 0;
        }
        if (mirrValuesAreAllPositives) {
            throw new EvaluationException(ErrorEval.DIV_ZERO);
        }

        return mirr(mirrValues, financeRate, reinvestRate);
    }

    private static double mirr(double[] in, double financeRate, double reinvestRate) {
        double value = 0;
        double numOfYears = in.length - 1;
        double pv = 0;
        double fv = 0;

        int indexN = 0;
        for (double anIn : in) {
            if (anIn < 0) {
                pv += anIn / Math.pow(1 + financeRate + reinvestRate, indexN++);
            }
        }

        for (double anIn : in) {
            if (anIn > 0) {
                fv += anIn * Math.pow(1 + financeRate, numOfYears - indexN++);
            }
        }

        if (fv != 0 && pv != 0) {
            value = Math.pow(-fv / pv, 1d / numOfYears) - 1;
        }
        return value;
    }
}