+ //+1 to avoid the singularity when bg<1 and p4>>1
+ //very^inf important! with this hesse NOTPOS->OK and no nan or inf in migrad
+ //i.e. numerically very stable
+ //the reason is when bg<1 ln blows up very fast with p4>>1 and nan/inf appears in migrad search
+ //the fitting will adjust the parameters as if bg is not shifted, the fitted curve looks fine!!
+ //-- 2012 Aug 8
+ //----> fail for 10h, not used, restore back!
+ //const Double_t lbg = TMath::Log(bg);
+
+ //redefine p2(<0) -> ln P2
+ //corresponds to alephFit.C fAlephOPt = 11
+ //const Double_t bb = p2 + TMath::Log( 1 + TMath::Exp(-p2-p4*lbg) );
+