Code Formulas

Below are code "formulas" for common tasks that come up when using ITensor. Please email us to suggest a formula you would like to see.

General Formulas

• Creating your own "driver" code that builds against ITensor
• Running your program in debug mode
• Reading input from a file
• Writing and reading ITensor objects to and from HDF5 files

ITensor Formulas

Formulas about working with ITensors, Index, etc.

• Evaluate a Function on Each Element of a Tensor
• Extract the Storage of a Dense ITensor
• Create a set of Site indices to use as a lattice
• Make a single-site operator (no quantum numbers)
• Exactly Compute the Ground State of a Small Hamiltonian
• Replace an ITensor Index with Another Index

MPS and DMRG Formulas

Formulas involving matrix product states and DMRG.

• MPS Basics & Updating MPS

  • Obtaining Elements or Components of a Tensor Represented as an MPS
  • Applying a one-site operator to an MPS
  • Applying a two-site 'gate' to an MPS

• Running DMRG

  • Perform a basic DMRG calculation
  • Perform a quantum number (QN) conserving DMRG calculation
  • Make a Ladder Hamiltonian for DMRG
  • Make a 2D Hamiltonian for DMRG
  • Compute excited states using DMRG
  • Read and write an MPS or MPO to and from disk
  • Stopping a DMRG Run "Gracefully"
  • Making a Custom DMRGObserver
  • Using a Mixed Site Set (Holstein Polaron Example)

• Measuring MPS

  • Measure local properties of an MPS wavefunction
  • Measure two-point correlator from an MPS wavefunction
  • Compute entanglement entropy
  • Measure spinless fermion two-point correlator
  • Compute a two-site reduced density matrix from an MPS
  • Operator matrix elements involving two MPS

• Time Evolution & Quantum Circuits

  • Time-evolving an MPS with Trotter Gates
  • Time-evolving an MPS with an MPO (matrix product operator)
  • Turning a set of gates into an MPO