Log[1.23] => 0.207014
Log[10] => Log[10]
Log[10,100] => 2
Log[E^4] => 4
Log[1 + I] => Log[1+I]
Log[1. + I] => 0.346574 + 0.785398 I
Ceiling[Pi] => 4
Floor[Pi] => 3
Sqrt[2] => Sqrt[2]
Sqrt[4] => 2
Sqrt[9/2] => 3/Sqrt[2]
Sqrt[3.5] => 1.87083
Sqrt[-5 + 12 I] => 2 + 3 I
Sqrt[-4] => 2I
Exp[2] => E^2
Exp[Log[4]] => 4