# PHP log() Function

PHPServer Side ProgrammingProgramming

## Definition and Usage

The log () function calculates natural logarithm of a number.

Logarithm is inverse of eponential. If 102=100, it means log10100=2. Natural logarithm is calculated with Euler Number e as base. In PHP, the predefined constant M_E gives value of e which is 2.7182818284590452354

For example, exp(4.60517018599)=100 (it is also same as e4.60517018599=100). Hence, loge100=4.60517018599

In PHP, loge is represented by log() function

## Syntax

log ( float $arg [, float$base = M_E ] ) : float


## Parameters

Sr.NoParameter & Description
1arg
The value whose logarithm is to be calculated
2base
Default value of base is M_E.

## Return Values

PHP log() function returns logarithm of arg to base. If base is not given, result is natural logarithm.

## PHP Version

This function is available in PHP versions 4.x, PHP 5.x as well as PHP 7.x.

## Example

Live Demo

Following example calculates natural logarithm of 100

<?php
$arg=100; echo "log(" .$arg . ")=" . log($arg); ?> ## Output This will produce following result − log(100)=4.6051701859881 ## Example Live Demo Following code calculates natural logarithm of 2. The result is equal to a predefined constant M_LN2 <?php$arg=2;
echo "log(" . $arg . ")=" . log($arg) . "\n";
echo "predefined constant M_LN2 : " . M_LN2
?>

## Output

This will produce following result −

log(2)=0.69314718055995
predefined constant M_LN2 : 0.69314718055995

## Example

Live Demo

Following example calculates log21024 and returns 10 −.

<?php
$arg=1024;$base=2;
echo "log(" . $arg . "," .$base . ")=" . log($arg,$base) . "\n";
?>

## Output

This will produce following result −

log(1024,2)=10

## Example

Live Demo

Similarly log2e results in predefined constant M_LOG2E

<?php
$arg=M_E;$base=2;
echo "log(" . $arg . "," .$base . ")=" . log($arg,$base) . "\n";
echo "predefined constant M_LOG2E = ". M_LOG2E;
?>

## Output

This will produce following result −

log(2.718281828459,2)=1.442695040889
predefined constant M_LOG2E = 1.442695040889