Fitting With Complex Fuctions

Hello,

I am trying to fit my data with the absolute value and phase of the following function:

TF1 *f=new TF1(“f”,"[0]*TMath::Exp([1]xTMath::Sqrt(-1)/2)*TMath::Erfc(TMath::Sqrt([1]xTMath::Sqrt(-1)/2))",-3,3)

My first attempt at using the absolute value of the function caused an error when I tried to use it to fit:

TF1 *rho=new TF1(“rho”,“TComplex::Abs([0]*TMath::Exp([1]xTMath::Sqrt(-1)/2)*TMath::Erfc(TMath::Sqrt([1]xTMath::Sqrt(-1)/2)))”,-3,3)

and I can not seem to use f.Theta() for fitting, could someone please tell me of my mistakes in these attemps?

Thank you!
Kirby