PHP log(): natural logarithm and custom bases

Calculate a logarithm

log() returns the natural logarithm by default. Supply a second argument when you need another valid logarithm base.

echo log(M_E);      // 1
echo log(8, 2);     // 3

For positive inputs, omit the second argument for the natural logarithm or provide a valid base greater than zero and not equal to one.

<?Php
echo log(2);// Output is 0.69314718055995
echo "<br>";
echo log(-1);// Output is NAN
echo "<br>";
echo log(0);// Output is -INF
echo "<br>";
echo log(5.7);// Output is 1.7404661748405
?>

Syntax

float log(float $num, float $base = M_E)

$num is the value whose logarithm is required. Omit $base for the natural logarithm.

LOG() with Base

<?Php
echo log(5,2);// Output is 2.3219280948874
echo "<br>";
echo log(5,10);// Output is 0.69897000433602 
echo "<br>";
echo log(5,2.7183);// Output is 1.609427153552
?>

e is the base of the natural logarithm and is approximately 2.718282.

For real-valued logarithms, $num should be positive. A custom base must be greater than zero and must not equal 1.

Example: Calculating Logarithms with Different Bases

$value = 100;
$base = 2;
$log_base2 = log($value, $base);  // Output: 6.643856
echo $log_base2;

Example: Handling Invalid Inputs

$value = -10;
$result = log($value);
if (is_nan($result)) {
    echo "Logarithm undefined for negative values.";
}

Output

Logarithm undefined for negative values.

Questions

What is the purpose of the log() function in PHP?
How is the log() function used to calculate the natural logarithm of a number?
What are the parameters of the log() function in PHP?
Can you specify a base other than e (natural logarithm) when using the log() function?
How can you calculate the logarithm to a different base using the log() function?
What does log() return for zero or a negative input?
What is the return value of the log() function when it is successful?
How can is_nan() and is_infinite() help check non-finite logarithm results?
Can the log() function be used to calculate the logarithm of complex numbers?
Are there any alternative functions or libraries available in PHP for more advanced logarithmic calculations?

Math Functions LOG10() function LOG1P() function

Subhendu Mohapatra

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LOG(): The logarithm of a number to base