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HMC documentation

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Peter Boyle 2018-09-25 23:28:17 +01:00
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documentation/_build/latex/Grid.pdf
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documentation/manual.rst
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@ -3189,7 +3189,127 @@ The exact one flavour algorithm for Domain Wall Fermions is present but is not d
HMC
=========================================
.. todo:: CD: The whole section needs to be completed, of course
There are a large number of examples under tests/hmc/
The most important data structure associated with (R)HMC describes the action
and integration scheme.
The action is a sum of terms, possibly with nested timesteps.
This is assembled in an ActionSet object (qcd/action/ActionSet.h).
The timesteps are managed by Levels. The ActionSet object maintains a list
of ActionLevel objects::
// Define the ActionSet
template <class GaugeField, class R>
using ActionSet = std::vector<ActionLevel<GaugeField, R> >;
Each ActionLevel is associated with each level of the
nested integration scheme, schematically::
template <class Field>
struct ActionLevel {
public:
unsigned int multiplier;
// Fundamental repr actions separated because of the smearing
typedef Action<Field>* ActPtr;
std::vector<ActPtr>& actions;
}
The outer loop, running MD trajectories, Metropolis steps, saving and restoring configurations
is generic and managed by a "Runner" class..
There are a number of possible integrators: LeapFrog, MinimumNorm2, ForceGradient
These are a template parameter to the HMCRunner class. We will take as an example Test_hmc_EODWFRatio.cc::
typedef GenericHMCRunner<MinimumNorm2> HMCWrapper; // Uses the default minimum norm
The test defines the Fermion action and Gauge action
typedef WilsonImplR FermionImplPolicy;
typedef DomainWallFermionR FermionAction;
typedef typename FermionAction::FermionField FermionField;
HMCWrapper TheHMC;
The HMC runner is given the Grid information (lifted from standard Grid --grid Lx.Ly.Lz.Lt command line)::
TheHMC.Resources.AddFourDimGrid("gauge");
The checkpointing strategy is defined::
// Checkpointer definition
CheckpointerParameters CPparams;
CPparams.config_prefix = "ckpoint_EODWF_lat";
CPparams.rng_prefix = "ckpoint_EODWF_rng";
CPparams.saveInterval = 5;
CPparams.format = "IEEE64BIG";
TheHMC.Resources.LoadNerscCheckpointer(CPparams);
.. todo:: HOW TO resume from saved RNGs. Guido changed this.
Random number generators are seeded::
RNGModuleParameters RNGpar;
RNGpar.serial_seeds = "1 2 3 4 5";
RNGpar.parallel_seeds = "6 7 8 9 10";
TheHMC.Resources.SetRNGSeeds(RNGpar);
Observables measured at the end of the trajectory can be registered::
// Construct observables
// here there is too much indirection
typedef PlaquetteMod<HMCWrapper::ImplPolicy> PlaqObs;
TheHMC.Resources.AddObservable<PlaqObs>();
The action must be defined::
RealD beta = 5.6 ;
WilsonGaugeActionR Waction(beta);
const int Ls = 8;
auto GridPtr = TheHMC.Resources.GetCartesian();
auto GridRBPtr = TheHMC.Resources.GetRBCartesian();
auto FGrid = SpaceTimeGrid::makeFiveDimGrid(Ls,GridPtr);
auto FrbGrid = SpaceTimeGrid::makeFiveDimRedBlackGrid(Ls,GridPtr);
LatticeGaugeField U(GridPtr);
Real mass = 0.04;
Real pv = 1.0;
RealD M5 = 1.5;
FermionAction DenOp(U,*FGrid,*FrbGrid,*GridPtr,*GridRBPtr,mass,M5);
FermionAction NumOp(U,*FGrid,*FrbGrid,*GridPtr,*GridRBPtr,pv, M5);
double StoppingCondition = 1.0e-8;
double MaxCGIterations = 10000;
ConjugateGradient<FermionField> CG(StoppingCondition,MaxCGIterations);
TwoFlavourEvenOddRatioPseudoFermionAction<FermionImplPolicy> Nf2(NumOp, DenOp,CG,CG);
// Set smearing (true/false), default: false
Nf2.is_smeared = false;
// Collect actions
ActionLevel<HMCWrapper::Field> Level1(1);
Level1.push_back(&Nf2);
ActionLevel<HMCWrapper::Field> Level2(4);
Level2.push_back(&Waction);
TheHMC.TheAction.push_back(Level1);
TheHMC.TheAction.push_back(Level2);
And the HMC can be setup and run::
TheHMC.Parameters.MD.MDsteps = 20;
TheHMC.Parameters.MD.trajL = 1.0;
TheHMC.ReadCommandLine(argc, argv); // these can be parameters from file
TheHMC.Run(); // no smearing
This puts together the pieces of the previous sections (actions, Fermion operators, solver algorithms etc...) into a full application.
Development of the internals
========================================

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tests/hmc/Test_hmc_EODWFRatio.cc
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@ -146,13 +146,7 @@ int main(int argc, char **argv) {
std::cout << GridLogMessage << "Denominator report, Dw(m) term (includes CG) : " << std::endl;
DenOp.Report();
Grid_finalize();
} // main