Difference between revisions of "Tutorials:Parameters"

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==Additional parameters for exact diagonalizayion ==
==Additional parameters for exact diagonalization ==
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Revision as of 10:03, 30 March 2007

The following input parameters are common to most of the ALPS applications

Lattice defintion

ALPS applications on lattices specify the lattice with the following three parameters

Parameter Default Meaning
LATTICE_LIBRARY lattices.xml path to a file containing lattice descriptions
LATTICE name of the lattice, specified by dimensionality, extent and unit cell.
GRAPH as an alternative to a lattice, also a specific arbitrary graph defined in the lattice library can be specified.

In addition, the lattice description can require further parameters (e.g. L or W) as specified in the lattice description file.

Model defintion

ALPS quantum lattice models can be specified using the following parameters

Parameter Default Meaning
MODEL_LIBRARY models.xml path to a file containing model descriptions</td>
MODEL name of the model (for example "spin" or "boson")

The model description can also require further parameters (e.g. S=1/2 or S=1, h=0.5 for spin models, t=1.5 or mu=0.5 for boson models) as specified in the model description file.

Parameters for finite temperature simulations

Parameter Meaning
T the temperature
BETA inverse of temperature (if temperature is not given

Additional parameters for Monte Carlo simulations

Parameter Default Meaning
SEED 0 The random number seed used in the next run. After using a seed in the creation of a Monte Carlo run, this value gets incremented by one.
WORK_FACTOR 1 A factor by which the work that needs to be done for a simulation is multiplied in load balancing.
SWEEPS number of Monte Carlo steps (after thermalization)
THERMALIZATION Number of Monte Carlo sweeps for thermalization

Additional parameters for exact diagonalization

Parameter Default Meaning
CONSERVED_QUANTUMNUMBERS specifies conserved global quantum numbers which are used to split the computation into smaller computations for the different sectors. If more than one quantum number is conserved, the quantum numbers are listed in double quotes and separated by commas as in CONSERVED_QUANTUMNUMBERS="N,Sz"
N_total, Sz_total, ... and similar parameters might be defined for your model through a constraint in your model definition. These constraints will be used if these parameters are specified and the quantumnumber is listed in CONSERVED_QUANTUMNUMBERS.
TRANSLATION_SYMMETRY true sparsediag exploits translational symmetry and classifies eigenstates by their momentum quantum numbers when possible. This symmetry reductions can be switched off with TRANSLATION_SYMMETRY=false.
TOTAL_MOMENTUM fixes the value of the total momentum. Further explanations can be found below.

If the lattice supports translation symmetries, you can specify the total momentum quantum numbers, but you should be quite careful in doing so.

TOTAL_MOMENTUM takes the momentum quantum numbers as a vector, i.e. a space-separated list of numbers. Typically, each momentum quantum number ki will be of the form

ki = 2 π ni/Li ,

where ni is an integer and Li the linear extent in the corresponding direction. It is possible to specify a symbolic number such as 2*Pi/5 if you put the values in quotation marks, e.g. TOTAL_MOMENTUM="2*Pi/5 0".

Warning: An illegal value of TOTAL_MOMENTUM may lead to incorrect results without any further error