pow

(PHP 4, PHP 5)

pow — 거듭제곱 표현

설명

number pow ( number $base , number $exp )

base 의 exp 승을 반환합니다.

Warning

PHP 4.0.6까지 pow()는 항상 float를 반환하였고, 경고를 발생하지 않았습니다.

인수

base: 사용할 밑
exp: 승수

반환값

base 의 exp 승. 결과가 정수로 표현될 수 있으면 integer형으로 반환하고, 그렇지 않으면 float형으로 반환합니다. 거듭제곱을 계산할 수 없으면 FALSE를 반환합니다.

변경점

버전	설명
4.0.6부터	가능하면 결과를 interger로 반환합니다. 이전에는 항상 float로 결과를 반환했습니다. 오래된 버전에서는 복잡한 수에 대해서 이상한 결과를 얻을 수도 있습니다.
4.2.0부터	PHP가 값을 계산할 수 없을 때, 경고를 발생하지 않습니다. 조용히 `FALSE`만 반환합니다.

예제

Example #1 pow()의 몇몇 예제


<?php

var_dump(pow(2, 8)); // int(256)
echo pow(-1, 20); // 1
echo pow(0, 0); // 1

echo pow(-1, 5.5); // PHP >4.0.6  NAN
echo pow(-1, 5.5); // PHP <=4.0.6 1.#IND
?>

참고

exp() - e의 누승을 계산
sqrt() - 평방 제곱근
bcpow() - 임의 정밀도 수 거듭제곱
gmp_pow() - Raise number into power

rad2deg

Last updated: Fri, 24 Jul 2009

add a note User Contributed Notes
pow

Matt Dudley
17-Jul-2008 07:14


Calculate wind chill based on the National Weather Service formula.



$temp = 25;

$wind_speed_mph = 6;



$wind_chill = 35.74+(.6215*$temp_f)-(35.75*(pow($wind_speed_mph, 0.16)))+(.4275*$temp_f*(pow($wind_speed_mph, 0.16)));



Value only valid when the temp is 45 or below.... I used this with a weather script I wrote that reads an xml file. They don't provide wind chill.

Docey
05-May-2007 02:33


no integer breaking here, pow just silently switches to using floats instead of integers.





pow(2, 31) = integer value


pow(2, 32) = float value.





the manual says the limit for floats is machine dependent so i did a little loop to see how far it will go before becomming infinit. the result is 1023.





pow(2, 1023) = float


pow(2, 1024) = ifinit.





tested on php 4.4.1 under windows2000 on an AMD AthlonXP 2800+.

gilthansREMOVEME at gmail dot com
16-Dec-2006 12:50


Note that pow(0, 0) equals to 1 on PHP 4 (only tested it there), although mathematically this is undefined.

moikboy (nospam) moikboy (nospam) hu
10-May-2006 05:27


Here is a function for calculating the $k-th root of $a :



<?php

function root($a,$k){return(($a<0&&$k%2>0)?-1:1)*pow(abs($a),1/$k);};

?>

louis [at] mulliemedia.com
01-Jan-2005 01:02


Here's a pow() function that allows negative bases :

<?php

function npow($base, $exp)

{

    $result = pow(abs($base), $exp);

    if ($exp % 2 !== 0) {

        $result = - ($result);

    } 

    return $result;

} 

?>

janklopper .AT. gmail dot.com
10-Nov-2004 11:26


since pow doesn't support decimal powers, you can use a different sollution,



thanks to dOt for doing the math!



a^b = e^(b log a)

which is no the 10log but the e-log (aka "ln")



so instead of: pow( $a , 0.6 ) use something like: exp( 0.6 * log($a) )

matthew underscore kay at ml1 dot net
18-Mar-2004 04:03


As of PHP5beta4, pow() with negative bases appears to work correctly and without errors (from a few cursory tests):



pow(-3, 3) = -27

pow(-3, 2) = 9

pow(-5, -1) = -0.2

bishop
18-Jul-2003 12:01


A couple of points on pow():

1. One of the official examples of pow(2,8) is not pragmatic; use 1 << 8 as it's substantially faster

2. When passing variables to pow(), cast them otherwise you might get warnings on some versions of PHP

3. All the rules of algebra apply: b**(-e) is 1/(b**e), b**(p/q) is the qth root of b**p



So, e.g., sqrt($x) === pow($x, .5); but sqrt() is faster.

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rad2deg

Last updated: Fri, 24 Jul 2009