Update variance record holder inside of single_dmrg_step()
Update variance record holder inside of single_dmrg_step()


Former-commit-id: fef4375e163a7d65700e5978ae685fb0d8006966
DavidAce/DMRG,DavidAce/DMRG,DavidAce/DMRG,DavidAce/DMRG