.. highlight:: none

Usage of ``tenes_std``
--------------------------------

``tenes_std`` is a tool to calculate imaginary time evolution operators :math:`\exp \left( -\tau \mathcal{H}_{ij} \right)` from a given Hamiltonian :math:`\mathcal{H}` and an imaginary time step :math:`\tau`, and to generate an input file for ``tenes``.

.. code:: bash

   $ tenes_std std.toml


- Takes input files as arguments
   - Multiple input files can be specified
   - When parameters are duplicated, ``tenes_std`` stops with an error
   - Sections that can be specified multiple times, such as ``[[observable.onesite]]``, can be specified in multiple input files simultaneously
      - In this case, the sections in the latter input file are appended to those in the former input file
- Output an input file for ``tenes``
- Command line options are as follows
   - ``--help``
      - Show help message
   - ``--version``
      - Show version number
   - ``--output=filename``
      - Specify the output file name ``filename``
      - Default is ``input.toml``
      - File name cannot be the same as the input file name

By making and editing input files, users can simulate on other models and lattices than predefined ones.	
See :ref:`sec-std-format` for details of the input file.
Below, a sample file for the S=1/2 Heisenberg model on the square lattice is shown.

::

   [parameter]
   [parameter.general]
   is_real = true   # limit tensors as real-valued ones
   [parameter.simple_update]
   num_step = 1000  # number of steps
   tau = 0.01       # imaginary time step
   [parameter.full_update]
   num_step = 0     # number of steps
   tau = 0.01       # imaginary time step
   [parameter.ctm]
   dimension = 9    # bond dimension

   [tensor]
   type = "square lattice"
   L_sub = [2, 2]   # unitcell size
   skew = 0         # boundary condition

   # tensors in unitcell
   [[tensor.unitcell]]
   index = [0, 3]   # index of tensors
   physical_dim = 2 # physical bond dimension
   virtual_dim = [3, 3, 3, 3]
                    # virtual bond dimension
   noise = 0.01     # noise in initial tensor
   initial_state = [1.0, 0.0]
                    # initial state

   [[tensor.unitcell]]
   index = [1, 2]
   physical_dim = 2
   virtual_dim = [3, 3, 3, 3]
   noise = 0.01
   initial_state = [0.0, 1.0]


   # (bond) hamiltonian
   [[hamiltonian]]
   dim = [2, 2]    # physical bond dimensions
   bonds = """     # bond information
   0 1 0           # first: index of one site
   1 1 0           # second: x coord of the other
   2 1 0           # third:  y coord of the other
   3 1 0
   0 0 1
   1 0 1
   2 0 1
   3 0 1
   """
   elements = """     # nonzero elements of tensor
   0 0 0 0 0.25 0.0   # first:  initial state of one site
   1 0 1 0 -0.25 0.0  # second: initial state of the other
   0 1 1 0 0.5 0.0    # third:  final state of one site
   1 0 0 1 0.5 0.0    # fourth: final state of the other 
   0 1 0 1 -0.25 0.0  # fifth:  real part
   1 1 1 1 0.25 0.0   # sixth:  imag part
   """

   # observables
   [observable]
   [[observable.onesite]]
   name = "Sz"        # name
   group = 0          # index
   sites = []         # sites to be acted
   dim = 2            # dimension
   elements = """     # nonzero elements
   0 0 0.5 0.0
   1 1 -0.5 0.0
   """

   [[observable.twosite]]
   name = "hamiltonian"
   group = 0
   dim = [2, 2]
   bonds = """
   0 1 0
   1 1 0
   2 1 0
   3 1 0
   0 0 1
   1 0 1
   2 0 1
   3 0 1
   """
   elements = """
   0 0 0 0 0.25 0.0
   1 0 1 0 -0.25 0.0
   0 1 1 0 0.5 0.0
   1 0 0 1 0.5 0.0
   0 1 0 1 -0.25 0.0
   1 1 1 1 0.25 0.0
   """

   [[observable.twosite]]
   name = "SzSz"
   group = 1
   dim = [2, 2]
   bonds = """
   0 1 0
   1 1 0
   2 1 0
   3 1 0
   0 0 1
   1 0 1
   2 0 1
   3 0 1
   """
   ops = [0, 0]  # index of onesite operators