Grid/Grid/qcd/hmc/UsingHMC.md

Using HMC in Grid

These are the instructions to use the Generalised HMC on Grid as of commit 749b802. Disclaimer: Grid is still under active development so any information here can be changed in future releases.

Command line options

(relevant file GenericHMCrunner.h) The initial configuration can be changed at the command line using --StartingType STARTING_TYPE, where STARTING_TYPE is one of HotStart, ColdStart, TepidStart, and CheckpointStart. Default: --StartingType HotStart

Example:

./My_hmc_exec  --StartingType HotStart

The CheckpointStart option uses the prefix for the configurations and rng seed files defined in your executable and the initial configuration is specified by --StartingTrajectory STARTING_TRAJECTORY, where STARTING_TRAJECTORY is an integer. Default: --StartingTrajectory 0

The number of trajectories for a specific run are specified at command line by --Trajectories TRAJECTORIES, where TRAJECTORIES is an integer. Default: --Trajectories 1

The number of thermalization steps (i.e. steps when the Metropolis acceptance check is turned off) is specified by --Thermalizations THERMALIZATIONS, where THERMALIZATIONS is an integer. Default: --Thermalizations 10

Any other parameter is defined in the source for the executable.

HMC controls

The lines

  std::vector<int> SerSeed({1, 2, 3, 4, 5});
  std::vector<int> ParSeed({6, 7, 8, 9, 10});

define the seeds for the serial and the parallel RNG.

The line

  TheHMC.MDparameters.set(20, 1.0);// MDsteps, traj length

declares the number of molecular dynamics steps and the total trajectory length.

Actions

Action names are defined in the directory Grid/qcd/action.

Gauge actions list (from Grid/qcd/action/gauge/Gauge.h):

WilsonGaugeActionR;
WilsonGaugeActionF;
WilsonGaugeActionD;
PlaqPlusRectangleActionR;
PlaqPlusRectangleActionF;
PlaqPlusRectangleActionD;
IwasakiGaugeActionR;
IwasakiGaugeActionF;
IwasakiGaugeActionD;
SymanzikGaugeActionR;
SymanzikGaugeActionF;
SymanzikGaugeActionD;

ConjugateWilsonGaugeActionR;
ConjugateWilsonGaugeActionF;
ConjugateWilsonGaugeActionD;
ConjugatePlaqPlusRectangleActionR;
ConjugatePlaqPlusRectangleActionF;
ConjugatePlaqPlusRectangleActionD;
ConjugateIwasakiGaugeActionR;
ConjugateIwasakiGaugeActionF;
ConjugateIwasakiGaugeActionD;
ConjugateSymanzikGaugeActionR;
ConjugateSymanzikGaugeActionF;
ConjugateSymanzikGaugeActionD;

Each of these action accepts one single parameter at creation time (beta). Example for creating a Symanzik action with beta=4.0

  SymanzikGaugeActionR(4.0)

Scalar actions list (from Grid/qcd/action/scalar/Scalar.h):

ScalarActionR;
ScalarActionF;
ScalarActionD;

The suffixes R, F, D in the action names refer to the Real (the precision is defined at compile time by the --enable-precision flag in the configure), Float and Double, that force the precision of the action to be 32, 64 bit respectively.