// psi((2m+1)/2) -> 2/(2m+1) + 2/2m +...+ 2/1 - Euler - 2log(2)
numeric rat(0);
for (numeric i((nx+_num_1())*_num2()); i.is_positive(); i-=_num2())
- rat += _num2()*i.inverse();
- return rat-Euler-_ex2()*log(_ex2());
+ rat += _num2()*i.inverse();
+ return rat-Euler-_ex2()*log(_ex2());
} else {
// use the recurrence relation
// psi(-m-1/2) == psi(-m-1/2+1) - 1 / (-m-1/2)