September 2017 - Comp-phys-alps-users

measuring truncation errors in mps_optim
by Robertson Esperanza 07 Dec '17

07 Dec '17

Thank you for all the help so far, now I'm trying to check for convergence of my results. First, is it enough to just check how the truncation error changes with sweeps (at a certain MAXSTATE value) or I need to both check the iteration history of the ground state energy and the truncation error? Second, checking the supplementary materials provided (Computer Physics Communications 185 (2014) 3430–3440) for the Hubbard ladder, why are there 381 values of energy and truncation weights for every iteration? Why is the total truncation error for that iteration is the sum of all the 381 truncation weight values (based on iteration.py)? How is truncation error defined (e.g. is it 1 - sum of all reduced density eigenvalues corresponding to all the picked states?) ? As far as I understand the DMRG algorithm every iteration/sweep has a corresponding bond dimension in which as you progress through iterations (until you reach the "SWEEPS"th iteration), bond dimension increases until you reach "MAXSTATES" at the "SWEEPS"th iteration. Regards, Robertson Esperanza

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alps mps application can not spawn threads with OpenMP when I use slurm
by Sun Rongyang 26 Sep '17

26 Sep '17

Dear all, The amazing mps code (mps_evolve and mps_optim) works very well with OpenMP on a node of a cluster when I start the task by hand. It can spawn many threads and calculate very fast. But when I wrote a sbatch script to commit a job to cluster by slurm, the mps applications can only use one thread and calculate very slowly. The sbatch script is shown as ----------------------------------------------------------------- #!/bin/bash #SBATCH --job-name=test_alps_omp #SBATCH --output=test_alps_omp.out #SBATCH --ntasks=1 #SBATCH --cpus-per-task=4 export OMP_NUM_THREADS=$SLURM_CPUS_PER_TASK mps_evolve test_alps_omp.in.xml ----------------------------------------------------------------- Does anyone have any idea about it? Thanks a lot! Beat regards, Rongyang Sun ----------------------------------------------------------------- Rongyang Sun Ph.D. Candidate Theoretical Quantum Matter Physics Institute for Advanced Study, Tsinghua University, Beijing 100084, China E-mail: sunry15(a)mails.tsinghua.edu.cn; sun-rongyang(a)outlook.com

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pairing correlation
by Chia-Chen Chang 15 Sep '17

15 Sep '17

Greetings ALPS users. For benchmark purposes, I'm interested in getting superconducting pair correlation functions on small clusters using ALPS' exact diagonalization library. If this is doable, I am wondering if there is a way to define extended operators such as d-wave or p-wave pair field operators? Thanks for your help! Chiachen Chang

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Eigenvalues of the reduced density matrix using MPS
by Desmond 11 Sep '17

11 Sep '17

Hi everyone, I'm wondering if we can get information regarding the eigenvalues of the reduced density matrix during the calculation. I understand that the entanglement entropy can be measured in the latest versions. However, it would be useful if we could extract the eigenvalues themselves. That would allow us to analyze the entanglement spectrum and more. Best, Desmond

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[ALPS] Randomized parameter per site
by John Ian Kenneth E. Felismino 05 Sep '17

05 Sep '17

Hi! Is it possible to have a site-dependent random parameter using DMRG in ALPS? For example in every a different random value for the Magnetic Field Strength acting on the model is assigned to each site. Thanks, Ian Felismino

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Total particle number can not be conserved using ALPS TEBD simulation
by Sun Rongyang 02 Sep '17

02 Sep '17

Dear ALPS users, When I follow the ALPS TEBD tutorial about hard-core boson model(http://alps.comp-phys.org/mediawiki/index.php/ALPS_2_Tutorials:TEBD-0… by Python, I measured the average particle number for each site, i.e. 'Avg Number' except the 'Loschmidt Echo' and 'V' by the following python code: data = pyalps.load.loadTimeEvolution(pyalps.getResultFiles(prefix='1D_HardcoreBosonModel'), measurements=['Loschmidt Echo', 'V', 'Avg Number']) Then I found the 'Avg Number' equals 0.3! This means that the total particle number is 0.3*10=3, not 5. In the tutorial, the conserved quantum number is 'N_total': 5. When I change the 'N_total' to 1 and 10, I got the same 'Avg Number'=0.3 Can any one give me some help? Thanks a lot! Best regards, Rongyang Sun ----------------------------------------------------------------- Rongyang Sun Ph.D. Candidate Theoretical Quantum Matter Physics Institute for Advanced Study, Tsinghua University, Beijing 100084, China E-mail: sunry15(a)mails.tsinghua.edu.cn; sun-rongyang(a)outlook.com

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