log2()
log2(\Complex\Complex|mixed  $complex) : \Complex\Complex
                Returns the base-2 logarithm of a complex number.
Parameters
| \Complex\Complex|mixed | $complex | Complex number or a numeric value. | 
Throws
- \Complex\Exception
- If argument isn't a valid real or complex number. 
- \InvalidArgumentException
- If the real and the imaginary parts are both zero 
Returns
\Complex\Complex —The base-2 logarithm of the complex argument.