# PHP Math - log() Function

The PHP Math log() function returns the natural logarithm or logarithm to the specified base of a given number. In special cases it returns the following:

• If any of the argument is NAN or first argument is less than zero, then the result is NAN.

### Syntax

```log(number, base)
```

### Parameters

 `number` `Required. ` Specify the number. `base` `Optional. ` Specify the base. Default is e

### Return Value

Returns the natural logarithm or logarithm to the specified base of a given number.

### Example:

In the example below, log() function is used to calculate the natural logarithm of a given number.

```<?php
echo "log(0) = ".log(0)."\n";
echo "log(0.5) = ".log(0.5)."\n";
echo "log(1) = ".log(1)."\n";
echo "log(10) = ".log(10)."\n";
echo "log(100) = ".log(100)."\n";
echo "log(INF) = ".log(INF)."\n";
echo "log(-INF) = ".log(-INF)."\n";
echo "log(NAN) = ".log(NAN)."\n";
?>
```

The output of the above code will be:

```log(0) = -INF
log(0.5) = -0.69314718055995
log(1) = 0
log(10) = 2.302585092994
log(100) = 4.6051701859881
log(INF) = INF
log(-INF) = NAN
log(NAN) = NAN
```

### Example:

Consider one more example where log() function is used to calculate the logarithm to the specified base of a given number. Please note that the base must be a positive number.

```<?php
//base 10
echo "log(0, 10) = ".log(0, 10)."\n";
echo "log(0.5, 10) = ".log(0.5, 10)."\n";
echo "log(1, 10) = ".log(1, 10)."\n";
echo "log(10, 10) = ".log(10, 10)."\n";
echo "log(100, 10) = ".log(100, 10)."\n";

//base 2
echo "\nlog(0, 2) = ".log(0, 2)."\n";
echo "log(0.5, 2) = ".log(0.5, 2)."\n";
echo "log(1, 2) = ".log(1, 2)."\n";
echo "log(16, 2) = ".log(16, 2)."\n";
echo "log(256, 2) = ".log(256, 2)."\n";
?>
```

The output of the above code will be:

```log(0, 10) = -INF
log(0.5, 10) = -0.30102999566398
log(1, 10) = 0
log(10, 10) = 1
log(100, 10) = 2

log(0, 2) = -INF
log(0.5, 2) = -1
log(1, 2) = 0
log(16, 2) = 4
log(256, 2) = 8
```

❮ PHP Math Functions

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