sinh
This is interesting. The "xth square root" idea is being used by a couple different posters, but it's not a root at all. It the logarithm, base x. In the posted code, it's rounded down to the next smaller or equal integer, but it's still a logarithm.
The full exact value as a float can be computed with log(value)/log(x). No loops needed.
For true xth roots, use pow(value, 1.0/x). That gives you the number that produces (value) when raised to the x power.
sqrt
(PHP 4, PHP 5)
sqrt — 平方根
説明
float sqrt
( float
$arg
)
arg の平方根を返します。
パラメータ
-
arg -
処理する引数。
返り値
arg の平方根を返します。
負の数を指定した場合は、特別な値 NAN を返します。
例
例1 sqrt() の例
<?php
// 小数点以下の精度は、precision ディレクティブの設定に依存します
echo sqrt(9); // 3
echo sqrt(10); // 3.16227766 ...
?>
add a note
User Contributed Notes
sqrt
Husoski
16-Feb-2012 11:04
wietse89 at gmail dot com
27-Nov-2009 12:15
For the second square root this code will work too:
Note that it doesn't return float values.
<?php
$new = strlen(decbin(256));
echo $new; //8
?>
btharper1221 at gmail dot com
15-May-2005 08:48
this is something you can use if you need an exact answer to a root problem, this includes an echo outside of the function to show how it works, it will return it such as
$ret[0] is the number still part of the root (this is the exactness part of it)
$ret[1] is the number of roots and
$ret[2] is 1 or 0, 1 being that there should be an i following the number of roots (imaginary)
<?php
function newrt($val,$rt){
$i = 0;
if(($rt % 2 == 0) && ($val < 1)){
$i = 1;
$val = (-$val);
}
$c = 1;
if(($rt % 2 != 0) && ($val < 0)){
$c = -$c;
$val = -$val;
}
for($d = 2; pow($d,$rt) <= abs($val); $d++){
if($val % (pow($d,$rt)) == 0){
$val = ($val/(pow($d,$rt)));
$c = ($c*$d);
$d--;
}
}
$ret[0] = $val;
$ret[1] = $c;
$ret[2] = $i;
return $ret;
}//end function newrt
$ret = newrt($num,$num2);
if($ret[0] != 1){
if($ret[2] == 0) echo $ret[1]." roots of ".$ret[0];
if($ret[2] == 1) echo $ret[1]."<b><i>i</i></b> roots of ".$ret[0];
}elseif($ret[0] == 1){
if($ret[2] == 0) echo $ret[1];
if($ret[2] == 1) echo "$ret[1]<b><i>i</i></b>";
}
?>
chris DOT rutledge AT gmail DOT com
31-Mar-2005 02:24
Just a note to say you can take the square root of a negative number - it returns an imaginary number.
One might do it like this
//take initial value of $x
$abs_x = abs($x);
$answer = sqrt($abs_x);
echo $answer;
if ($x < 0) echo"<b><i>i</i></b>";
jouhni at web dot de
17-Feb-2005 11:46
To get any root of a number your can use the pow() function:
pow(8, 1/3)
which gives you the third root of eight.
Jouhni
bishop
17-Jul-2003 10:09
Compute a triangle's area:
function triangleArea($a, $b /* ... */) {
if (func_num_args() === 3) {
$s = .5 * ($a + $b + ($c = func_get_arg(2)));
return sqrt($s * ($s-$a) * ($s-$b) * ($s-$c));
} else {
return (.5 * $a * $b);
}
}
With 2 args, parameters are triangle's base and height. With 3 args, parameters are the lengths of each side. Argument order is not important.
Either way, you get the area.