Function table where evaluation is carried out using reals and never complex numbers.
Evaluating sqrt(-1) will return NaN rather than a complex number.
Function asin(2), acos(2), acosh(0.5), atanh(2), ln(-1), log(-1), lg(-1)
also returns NaN. Furthermore, the constant i is not defined.
Returns a new shallow copy of this function table.
The entries in the table refer to the the same instances of the postfix math commands.
If sub-classes use pfmc's which are not thread safe
they should override this methods and set a new instance for the table.