log
Returns the natural logarithm (base e) of a double value. Special cases:
If the argument is NaN or less than zero, then the result is NaN.
If the argument is positive infinity, then the result is positive infinity.
If the argument is positive zero or negative zero, then the result is negative infinity.
If the argument is
1.0, then the result is positive zero.
Return
the value ln a, the natural logarithm of a.
Parameters
a
a value