function f=chi_voigt(beta,x)
% Doppler chi function in term of Voigt function
% (c) 2015 Alain Hebert, Ecole Polytechnique de Montreal
   Fad_w=@(z) exp(-z^2)*double(erfc(sym(-z*1i)));
   if (beta == 0)
     f=x/(1+x^2);
   else
     f=sqrt(pi)*imag(Fad_w((x+1i)/beta))/beta;
   end