0 votes
asked ago by (120 points)

Hi Miles,

Thank you for your wonderful work on the ITensor package. I had a few questions about the truncation error in connection with extrapolating the energy E with \epsilon as described in your paper [arXiv: 1105.1374]:

  1. Calling the function dmrg returns the ground-state energy and the wavefunction, but is there an easy way to return the truncation error as well? I see that \epsilon is printed out (but not returned) as a part of the function call and I was wondering if there is a more direct way of obtaining it.

  2. Suppose we set sweeps.cutoff() = 1E-12. Then, would the correct extrapolation technique be to gradually increase m in sweeps.maxm() and for each case, record the energies together with the errors (which should be less than 1E-12)? However, if m is initially not large enough, how does the algorithm ensure that the truncation error is always < 10^{-12}?

  3. Finally, in your paper, you mention that normally a linear extrapolation of E versus \epsilon is best. Do the excited state energies also scale the same way, i.e. linearly?

Thanks a lot for your time!


Please log in or register to answer this question.

Welcome to ITensor Support Q&A, where you can ask questions and receive answers from other members of the community.

Formatting Tips:
  • To format code, indent by four spaces
  • To format inline LaTeX, surround it by @@ on both sides
  • To format LaTeX on its own line, surround it by $$ above and below
  • For LaTeX, it may be necessary to backslash-escape underscore characters to obtain proper formatting. So for example writing \sum\_i to represent a sum over i.
If you cannot register due to firewall issues (e.g. you cannot see the capcha box) please email Miles Stoudenmire to ask for an account.

To report ITensor bugs, please use the issue tracker.