PHP log()函数

log()函数是PHP内置函数，用于计算一个数的自然对数或以某个基数为底的对数。

语法

log(number,base);

注意：如果输入的数字具有基数Y（可选），我们会得到以X为底的LOG输出。

示例1

<?php
num=2;
echo "Your number is: ".num;
echo "<br>"."By using log() function your number is : ".log($num);
?>

输出：

Your number is: 2
By using log() function your number is : 0.69314718055995

示例2

<?php
num=2.7183;
echo "Your number is: ".num;
echo "<br>"."By using log() function your number is : ".log($num);
?>

输出:

Your number is: 2.7183
By using log() function your number is : 1.000006684914

示例3

<?php
num=-1;
echo "Your number is: ".num;
echo "<br>"."By using log() function your number is : ".log($num);
?> 

输出：

Your number is: -1
By using log() function your number is : NAN

示例4

<?php
num=0;
echo "Your number is: ".num;
echo "<br>"."By using log() function your number is : ".log($num);
?>

输出：

Your number is: 0
By using log() function your number is : -INF

注意：LOG（）与Base的示例。

示例5

<?php
echo "Your number is: log(5,2) ";
echo "<br>"."By using log() function your number is : ".log(5,2);
?>

输出：

Your number is: log(5,2) 
By using log() function your number is : 2.3219280948874

示例6

<?php
echo "Your number is: log(5,10) ";
echo "<br>"."By using log() function your number is : ".log(5,10);
?>

输出:

Your number is: log(5,10) 
By using log() function your number is : 0.69897000433602

示例7

<?php
echo "Your number is: log(5,2.7183) ";
echo "<br>"."By using log() function your number is : ".log(5,2.7183);
?>

输出：

Your number is: log(5,2.7183) 
By using log() function your number is : 1.609427153552