init

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

@@ -0,0 +1,132 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheet\Calculation\Statistical\Distributions;
+
+use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
+use PhpOffice\PhpSpreadsheet\Calculation\Exception;
+use PhpOffice\PhpSpreadsheet\Calculation\Functions;
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
+
+class StudentT
+{
+    use ArrayEnabled;
+
+    /**
+     * TDIST.
+     *
+     * Returns the probability of Student's T distribution.
+     *
+     * @param mixed $value Float value for the distribution
+     *                      Or can be an array of values
+     * @param mixed $degrees Integer value for degrees of freedom
+     *                      Or can be an array of values
+     * @param mixed $tails Integer value for the number of tails (1 or 2)
+     *                      Or can be an array of values
+     *
+     * @return array|float|string The result, or a string containing an error
+     *         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 $degrees, mixed $tails)
+    {
+        if (is_array($value) || is_array($degrees) || is_array($tails)) {
+            return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $degrees, $tails);
+        }
+
+        try {
+            $value = DistributionValidations::validateFloat($value);
+            $degrees = DistributionValidations::validateInt($degrees);
+            $tails = DistributionValidations::validateInt($tails);
+        } catch (Exception $e) {
+            return $e->getMessage();
+        }
+
+        if (($value < 0) || ($degrees < 1) || ($tails < 1) || ($tails > 2)) {
+            return ExcelError::NAN();
+        }
+
+        return self::calculateDistribution($value, $degrees, $tails);
+    }
+
+    /**
+     * TINV.
+     *
+     * Returns the one-tailed probability of the chi-squared distribution.
+     *
+     * @param mixed $probability Float probability for the function
+     *                      Or can be an array of values
+     * @param mixed $degrees Integer value for degrees of freedom
+     *                      Or can be an array of values
+     *
+     * @return array|float|string The result, or a string containing an error
+     *         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 inverse(mixed $probability, mixed $degrees)
+    {
+        if (is_array($probability) || is_array($degrees)) {
+            return self::evaluateArrayArguments([self::class, __FUNCTION__], $probability, $degrees);
+        }
+
+        try {
+            $probability = DistributionValidations::validateProbability($probability);
+            $degrees = DistributionValidations::validateInt($degrees);
+        } catch (Exception $e) {
+            return $e->getMessage();
+        }
+
+        if ($degrees <= 0) {
+            return ExcelError::NAN();
+        }
+
+        $callback = fn ($value) => self::distribution($value, $degrees, 2);
+
+        $newtonRaphson = new NewtonRaphson($callback);
+
+        return $newtonRaphson->execute($probability);
+    }
+
+    private static function calculateDistribution(float $value, int $degrees, int $tails): float
+    {
+        //    tdist, which finds the probability that corresponds to a given value
+        //    of t with k degrees of freedom. This algorithm is translated from a
+        //    pascal function on p81 of "Statistical Computing in Pascal" by D
+        //    Cooke, A H Craven & G M Clark (1985: Edward Arnold (Pubs.) Ltd:
+        //    London). The above Pascal algorithm is itself a translation of the
+        //    fortran algoritm "AS 3" by B E Cooper of the Atlas Computer
+        //    Laboratory as reported in (among other places) "Applied Statistics
+        //    Algorithms", editied by P Griffiths and I D Hill (1985; Ellis
+        //    Horwood Ltd.; W. Sussex, England).
+        $tterm = $degrees;
+        $ttheta = atan2($value, sqrt($tterm));
+        $tc = cos($ttheta);
+        $ts = sin($ttheta);
+
+        if (($degrees % 2) === 1) {
+            $ti = 3;
+            $tterm = $tc;
+        } else {
+            $ti = 2;
+            $tterm = 1;
+        }
+
+        $tsum = $tterm;
+        while ($ti < $degrees) {
+            $tterm *= $tc * $tc * ($ti - 1) / $ti;
+            $tsum += $tterm;
+            $ti += 2;
+        }
+
+        $tsum *= $ts;
+        if (($degrees % 2) == 1) {
+            $tsum = Functions::M_2DIVPI * ($tsum + $ttheta);
+        }
+
+        $tValue = 0.5 * (1 + $tsum);
+        if ($tails == 1) {
+            return 1 - abs($tValue);
+        }
+
+        return 1 - abs((1 - $tValue) - $tValue);
+    }
+}