### Strange timing data for DMRG applied to Fermi-Hubbard model

Posted:

**12 Feb 2024, 12:09**Hi All,

I am doing some DMRG calculations for the Fermi-Hubbard model using FermiHubbardModel(). I'm running the code on a cluster with 8 OMP threads and have been seeing some strange trends in the run time observed as I change the max bond dimension. In particular, certain values of chi_max seem to take wildly longer than others for no apparent reason. The data below are from a 4x4 square lattice with no pbc's, U=4, t=1, mu=0, svd_min=1e-10, max_E_err=1e-10 and the starting state is the Neel state:

chi_max, time

100, 75

200, 2007

300, 2572

400, 156

500, 182

600, 229

700, 292

800, 360

900, 428

1000, 510

1250, 610

1500, 2276

1750, 962

2000, 1151

2500, 1242

I have run these multiple times and even using the full node to myself and I see the same trend. I have also tried with just 1 and 2 OMP threads for the spurious points and observe the same trend. I installed tenpy from source and compiled it (without MKL). Does anyone know what could be causing values of e.g. chi_max = 300 to take longer than values that are as large as chi_max=2500?

Thank you

I am doing some DMRG calculations for the Fermi-Hubbard model using FermiHubbardModel(). I'm running the code on a cluster with 8 OMP threads and have been seeing some strange trends in the run time observed as I change the max bond dimension. In particular, certain values of chi_max seem to take wildly longer than others for no apparent reason. The data below are from a 4x4 square lattice with no pbc's, U=4, t=1, mu=0, svd_min=1e-10, max_E_err=1e-10 and the starting state is the Neel state:

chi_max, time

100, 75

200, 2007

300, 2572

400, 156

500, 182

600, 229

700, 292

800, 360

900, 428

1000, 510

1250, 610

1500, 2276

1750, 962

2000, 1151

2500, 1242

I have run these multiple times and even using the full node to myself and I see the same trend. I have also tried with just 1 and 2 OMP threads for the spurious points and observe the same trend. I installed tenpy from source and compiled it (without MKL). Does anyone know what could be causing values of e.g. chi_max = 300 to take longer than values that are as large as chi_max=2500?

Thank you