Dear, M. Dolfi

I am a freshman about DMRG. I have two questions :
(1) How to get truncation error using mps_optim codes ? 
(2) How to get von Neumann entanglement entropy S(A) of a system A. 
Actually, I  have obtained entanglement entropy data by setting MEASURE[Entropy]=1 using mps_optim. For a spin chain, we got  the data number of entanglement entropy which seems the same as the number of 'bond'  in chain. For example, to run a mps_optim of a spin chain with 32 sites , I will get 31 data in output of entropy. What meaning of such entanglement entropy data?
How to get von Neumann entanglement entropy S(A) of a two dimension system A (Just like page 5 in paper Phys.Rev.B 64,024424(2012))

L.J.Meng
Xiangtan University
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