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lib/PhpSpreadsheet/Calculation/Statistical/Distributions/Exponential.php

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+<?php
+
+namespace PhpOffice\PhpSpreadsheet\Calculation\Statistical\Distributions;
+
+use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
+use PhpOffice\PhpSpreadsheet\Calculation\Exception;
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+
+class Exponential
+{
+    use ArrayEnabled;
+
+    /**
+     * EXPONDIST.
+     *
+     *    Returns the exponential distribution. Use EXPONDIST to model the time between events,
+     *        such as how long an automated bank teller takes to deliver cash. For example, you can
+     *        use EXPONDIST to determine the probability that the process takes at most 1 minute.
+     *
+     * @param mixed $value Float value for which we want the probability
+     *                      Or can be an array of values
+     * @param mixed $lambda The parameter value as a float
+     *                      Or can be an array of values
+     * @param mixed $cumulative Boolean value indicating if we want the cdf (true) or the pdf (false)
+     *                      Or can be an array of values
+     *
+     * @return array|float|string If an array of numbers is passed as an argument, then the returned result will also be an array
+     *            with the same dimensions
+     */
+    public static function distribution(mixed $value, mixed $lambda, mixed $cumulative): array|string|float
+    {
+        if (is_array($value) || is_array($lambda) || is_array($cumulative)) {
+            return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $lambda, $cumulative);
+        }
+
+        try {
+            $value = DistributionValidations::validateFloat($value);
+            $lambda = DistributionValidations::validateFloat($lambda);
+            $cumulative = DistributionValidations::validateBool($cumulative);
+        } catch (Exception $e) {
+            return $e->getMessage();
+        }
+
+        if (($value < 0) || ($lambda < 0)) {
+            return ExcelError::NAN();
+        }
+
+        if ($cumulative === true) {
+            return 1 - exp(0 - $value * $lambda);
+        }
+
+        return $lambda * exp(0 - $value * $lambda);
+    }
+}