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POBigDecimal.pow() of negative number
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copied!<p>I just cannot find the correct answer, so here is my problem: I want to be able to calculate the indexation (<em>a positive or negative percentage</em>) over a <code>price</code> and <code>period</code>.</p> <p><strong>Expectations:</strong></p> <hr> <p><strong>Case #1</strong><br> Price : <strong>1.000,00</strong><br> Indexation percentage : <strong>5%</strong> </p> <p>Calculation over 5 years with positive percentage:</p> <pre><code>1. 1000 x 5^0 = 1000 2. 1000 x 5^1 = 1050 3. 1000 x 5^2 = 1102,50 4. 1000 x 5^3 = 1157.625 5. 1000 x 5^4 = 1215,50625 </code></pre> <p><strong>Case #2</strong><br> Price : <strong>1.000,00</strong><br> Indexation percentage : <strong>-5%</strong> </p> <p>Calculation over 5 years with negative percentage:</p> <pre><code>1. 1000 x -5^0 = 1000 2. 1000 x -5^1 = 950 3. 1000 x -5^2 = 902,50 4. 1000 x -5^3 = 857,375 5. 1000 x -5^4 = 814,50625 </code></pre> <p><strong>Results:</strong></p> <hr> <p>And this negative percentage goes wrong, because my java code prints this out:</p> <pre><code>1000 -5000 -125000 15625000 1175690408 </code></pre> <p>My code is pretty simple, i think:</p> <pre><code>BigDecimal percentageValue = new BigDecimal("-5"); BigDecimal indexation = percentageValue.divide(ONE_HUNDRED).add(BigDecimal.ONE); BigDecimal price = new BigDecimal("1000"); for (int i = 0; i < 5; i++) { price = price.multiply(indexation.pow(i)); System.out.println(price.intValue()); } </code></pre> <p><strong>Solution:</strong></p> <pre><code>static final BigDecimal ONE_HUNDRED = new BigDecimal("100"); public static void main(String[] args) { BigDecimal percentageValue = new BigDecimal("-5"); BigDecimal indexation = percentageValue.divide(ONE_HUNDRED).add(BigDecimal.ONE); BigDecimal price = new BigDecimal("1000"); for (int i = 0; i < 5; i++) { BigDecimal result = price.multiply(indexation.pow(i)); System.out.println(result); } } </code></pre>

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