Usage

Input Configuration File

Simulation parameters are read from a text configuration file. A convenient starting point is input/default.cfg, and additional examples are provided under input/. These files select the algorithm, model, system size, numerical thresholds, output settings, and related run parameters.

xDMRG++ reads a custom configuration file from the command line. A typical invocation is:

./xDMRG++ --config path/to/file.cfg

When using a preset build, the full command usually looks more like:

./build/release-cmake-flexiblas-native/xDMRG++ --config input/default.cfg

The full list of configuration namespaces and variables is documented under Settings.

Output Data File

Simulation results are written to an HDF5 file. The output path is set in the input configuration, and by default it is output/output.h5.

The contents of the file depend on the active storage policy. A typical output file may include:

  • Model parameters and run metadata.

  • Iteration tables, convergence information, and measurements.

  • Saved matrix product state data for later analysis.

  • State data needed to resume a simulation, when the relevant storage settings are enabled.

To inspect the data you can use any HDF5 viewer, such as HDF Compass or HDFView.

Model Hamiltonians

The code currently includes the following one-dimensional model Hamiltonians:

  • ModelType::ising_sdual: The self-dual transverse-field Ising model.

  • ModelType::ising_tf_rf: The transverse-field Ising model with random on-site field.

  • ModelType::ising_majorana: The Ising-Majorana model.

  • ModelType::xxz: The XXZ spin chain.

  • ModelType::lbit: The l-bit Hamiltonian, used to describe a many-body localized phase in terms of local integrals of motion.

These Hamiltonians are implemented as matrix product operators under source/tensors/model. The corresponding configuration variables live in source/config/settings.h, and the active model is selected in the input file with model::model_type.

Adding a new model currently means implementing a new MPO site class and deriving it from MpoSite, following the structure of the existing models.