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PHP log() Function
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.No | Parameter & Description |
|---|---|
| 1 | arg The value whose logarithm is to be calculated |
| 2 | base 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
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
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) . "
";
echo "predefined constant M_LN2 : " . M_LN2
?>Output
This will produce following result −
log(2)=0.69314718055995 predefined constant M_LN2 : 0.69314718055995
Example
Following example calculates log21024 and returns 10 −.
<?php
$arg=1024;
$base=2;
echo "log(" . $arg . "," . $base . ")=" . log($arg, $base) . "
";
?>Output
This will produce following result −
log(1024,2)=10
Example
Similarly log2e results in predefined constant M_LOG2E −
<?php
$arg=M_E;
$base=2;
echo "log(" . $arg . "," . $base . ")=" . log($arg, $base) . "
";
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
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