[Gretl-users] Re: Negative numbers to fractional powers

Let X be a series of negative numbers. Then the command series Y = X^(1/3) (or any other "1/oddnumber" fractional power) returns a "Warning: pow: Domain error" message, overwrites series "Y" and returns a "no valid values" if one attempts to view the series. Why is this happening, considering that X^(1/3) is a real number even if X is a negative number? Now, consider series "Z" which has both positive /and/ negative values. We want to compute W = Z^(1/3) Given a recent new feature in gretl, the sign function  sgn(), I guess we can avoid the obvious conditional if-else statement, and compute W  by writing W = sgn(Z) * (abs(Z)^(1/3)) that covers also the case of Z taking an exact zero value. Is this the proper/efficient way? -- Alecos Papadopoulos PhD Athens University of Economics and Business web: alecospapadopoulos.wordpress.com/ skype:alecos.papadopoulos