If the optional base parameter is specified,
log() returns logbasearg, otherwise log()
returns the natural logarithm of arg.
Note:
The base parameter became available
with PHP 4.3.0.
As always 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.
