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log EXPR
log

Returns the natural logarithm (base e) of EXPR. If EXPR is omitted, returns log of $_. To get the log of another base, use basic algebra: The base-N log of a number is is equal to the natural log of that number divided by the natural log of N. For example:

sub log10 {
    my $n = shift;
    return log($n)/log(10);
} 

See also "exp" for the inverse operation.