log() function in PHP

The log() function in PHP calculates the natural logarithm (base e) of a number. It can also calculate logarithms with a specified base when provided as the second parameter.

Syntax

log(number, base)

Parameters

• number − The value for which you want to calculate the logarithm (must be positive)

• base − Optional. The logarithmic base. If omitted, calculates natural logarithm (base e)

Return Value

Returns the logarithm of the number. Returns -INF for zero, NAN for negative numbers, and a float value for positive numbers.

Examples

Basic Natural Logarithm

Calculate the natural logarithm of 1 −

<?php
    echo log(1);
?>

0

Logarithm of Zero

When the input is zero, the function returns negative infinity −

<?php
    echo log(0);
?>

-INF

Multiple Values

Calculate logarithms of different numbers −

<?php
    echo log(10) . "<br>";
    echo log(2.7) . "<br>";
    echo log(exp(1)); // e^1 = e, so log(e) = 1
?>

2.302585092994
0.99325177301028
1

Using Custom Base

Calculate logarithm with base 10 and base 2 −

<?php
    echo log(100, 10) . "<br>";  // log base 10 of 100
    echo log(8, 2) . "<br>";     // log base 2 of 8
    echo log(27, 3);           // log base 3 of 27
?>

2
3
3

Conclusion

The log() function is essential for mathematical calculations involving logarithms. Use it with one parameter for natural logarithms or two parameters for custom base logarithms.