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(PHP 4, PHP 5)

logNatural logarithm


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

If the optional base parameter is specified, log() returns logbase arg, otherwise log() returns the natural logarithm of arg.



The value to calculate the logarithm for


The optional logarithmic base to use (defaults to 'e' and so to the natural logarithm).

Return Values

The logarithm of arg to base, if given, or the natural logarithm.


Version Description
4.3.0 The optional parameter base became available. For older versions you can calculate the logarithm in base b of a number n, but using the mathematical identity: logb(n) = log(n)/log(b), where log is the neperian (or natural) logarithm.

See Also

  • log10() - Base-10 logarithm
  • exp() - Calculates the exponent of e
  • pow() - Exponential expression

PHP Manual