poi/src/java/org/apache/poi/hssf/record/formula/functions/Npv.java

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   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       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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   See the License for the specific language governing permissions and
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package org.apache.poi.hssf.record.formula.functions;

import org.apache.poi.hssf.record.formula.eval.EvaluationException;

/**
 * Calculates the net present value of an investment by using a discount rate
 * and a series of future payments (negative values) and income (positive
 * values). Minimum 2 arguments, first arg is the rate of discount over the
 * length of one period others up to 254 arguments representing the payments and
 * income.
 * 
 * @author SPetrakovsky
 */
public class Npv extends NumericFunction.MultiArg {

	public Npv() {
		super(2, 255);
	}

	@Override
	protected double evaluate(double[] ds) throws EvaluationException {
		double rate = ds[0];
		double sum = 0;
		for (int i = 1; i < ds.length; i++) {
			sum += ds[i] / Math.pow(rate + 1, i);
		}
		return sum;
	}

}