Erratum: Transverse emittance preservation during bunch compression in the Fermi free electron laser [Phys. Rev. ST Accel. Beams 15, 020701 (2012)] - S. Di Mitri; E. M. Allaria; P. Craievich; W. Fawley; L. Giannessi; A. Lutman; G. Penco; S. Spampinati; M. Trovo (Physical Review Special Topics. Accelerators and Beams, 2012)