tablepress / libraries / vendor / PhpSpreadsheet / Calculation / Engineering / BesselK.php

BesselK.php in TablePress – Tables in WordPress made easy 3.4, at libraries/vendor/PhpSpreadsheet/Calculation/Engineering/BesselK.php

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1	<?php
2
3	namespace TablePress\PhpOffice\PhpSpreadsheet\Calculation\Engineering;
4
5	use TablePress\PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
6	use TablePress\PhpOffice\PhpSpreadsheet\Calculation\Exception;
7	use TablePress\PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
8
9	class BesselK
10	{
11	use ArrayEnabled;
12
13	/**
14	* BESSELK.
15	*
16	* Returns the modified Bessel function Kn(x), which is equivalent to the Bessel functions evaluated
17	* for purely imaginary arguments.
18	*
19	* Excel Function:
20	* BESSELK(x,ord)
21	*
22	* @param mixed $x A float value at which to evaluate the function.
23	* If x is nonnumeric, BESSELK returns the #VALUE! error value.
24	* Or can be an array of values
25	* @param mixed $ord The integer order of the Bessel function.
26	* If ord is not an integer, it is truncated.
27	* If $ord is nonnumeric, BESSELK returns the #VALUE! error value.
28	* If $ord < 0, BESSELKI returns the #NUM! error value.
29	* Or can be an array of values
30	*
31	* @return array<mixed>\|float\|string Result, or a string containing an error
32	* If an array of numbers is passed as an argument, then the returned result will also be an array
33	* with the same dimensions
34	*/
35	public static function BESSELK($x, $ord)
36	{
37	if (is_array($x) \|\| is_array($ord)) {
38	return self::evaluateArrayArguments([self::class, __FUNCTION__], $x, $ord);
39	}
40
41	try {
42	$x = EngineeringValidations::validateFloat($x);
43	$ord = EngineeringValidations::validateInt($ord);
44	} catch (Exception $e) {
45	return $e->getMessage();
46	}
47
48	if (($ord < 0) \|\| ($x <= 0.0)) {
49	return ExcelError::NAN();
50	}
51
52	$fBk = self::calculate($x, $ord);
53
54	return (is_nan($fBk)) ? ExcelError::NAN() : $fBk;
55	}
56
57	private static function calculate(float $x, int $ord): float
58	{
59	switch ($ord) {
60	case 0:
61	return self::besselK0($x);
62	case 1:
63	return self::besselK1($x);
64	default:
65	return self::besselK2($x, $ord);
66	}
67	}
68
69	/**
70	* Mollify Phpstan.
71	*
72	* @codeCoverageIgnore
73	*/
74	private static function callBesselI(float $x, int $ord): float
75	{
76	$rslt = BesselI::BESSELI($x, $ord);
77	if (!is_float($rslt)) {
78	throw new Exception('Unexpected array or string');
79	}
80
81	return $rslt;
82	}
83
84	private static function besselK0(float $x): float
85	{
86	if ($x <= 2) {
87	$fNum2 = $x * 0.5;
88	$y = ($fNum2 * $fNum2);
89
90	return -log($fNum2) * self::callBesselI($x, 0)
91	+ (-0.57721566 + $y * (0.42278420 + $y * (0.23069756 + $y * (0.3488590e-1 + $y * (0.262698e-2 + $y
92	* (0.10750e-3 + $y * 0.74e-5))))));
93	}
94
95	$y = 2 / $x;
96
97	return exp(-$x) / sqrt($x)
98	* (1.25331414 + $y * (-0.7832358e-1 + $y * (0.2189568e-1 + $y * (-0.1062446e-1 + $y
99	* (0.587872e-2 + $y * (-0.251540e-2 + $y * 0.53208e-3))))));
100	}
101
102	private static function besselK1(float $x): float
103	{
104	if ($x <= 2) {
105	$fNum2 = $x * 0.5;
106	$y = ($fNum2 * $fNum2);
107
108	return log($fNum2) * self::callBesselI($x, 1)
109	+ (1 + $y * (0.15443144 + $y * (-0.67278579 + $y * (-0.18156897 + $y * (-0.1919402e-1 + $y
110	* (-0.110404e-2 + $y * (-0.4686e-4))))))) / $x;
111	}
112
113	$y = 2 / $x;
114
115	return exp(-$x) / sqrt($x)
116	* (1.25331414 + $y * (0.23498619 + $y * (-0.3655620e-1 + $y * (0.1504268e-1 + $y * (-0.780353e-2 + $y
117	* (0.325614e-2 + $y * (-0.68245e-3)))))));
118	}
119
120	private static function besselK2(float $x, int $ord): float
121	{
122	$fTox = 2 / $x;
123	$fBkm = self::besselK0($x);
124	$fBk = self::besselK1($x);
125	for ($n = 1; $n < $ord; ++$n) {
126	$fBkp = $fBkm + $n * $fTox * $fBk;
127	$fBkm = $fBk;
128	$fBk = $fBkp;
129	}
130
131	return $fBk;
132	}
133	}
134