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https://github.com/paboyle/Grid.git
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98 lines
2.6 KiB
C++
98 lines
2.6 KiB
C++
#include <Grid.h>
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using namespace std;
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using namespace Grid;
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using namespace Grid::QCD;
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#define parallel_for PARALLEL_FOR_LOOP for
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int main (int argc, char ** argv)
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{
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Grid_init(&argc,&argv);
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std::vector<int> latt_size = GridDefaultLatt();
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std::vector<int> simd_layout = GridDefaultSimd(Nd,vComplex::Nsimd());
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std::vector<int> mpi_layout = GridDefaultMpi();
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GridCartesian Grid(latt_size,simd_layout,mpi_layout);
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GridRedBlackCartesian RBGrid(latt_size,simd_layout,mpi_layout);
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int threads = GridThread::GetThreads();
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std::cout<<GridLogMessage << "Grid is setup to use "<<threads<<" threads"<<std::endl;
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std::vector<int> seeds({1,2,3,4});
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GridParallelRNG pRNG(&Grid);
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pRNG.SeedRandomDevice();
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LatticeGaugeField U(&Grid);
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SU3::HotConfiguration(pRNG,U);
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double beta = 1.0;
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double c1 = 0.331;
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PlaqPlusRectangleActionR Action(beta,c1);
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// WilsonGaugeActionR Action(beta);
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ComplexD S = Action.S(U);
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// get the deriv of phidag MdagM phi with respect to "U"
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LatticeGaugeField UdSdU(&Grid);
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Action.deriv(U,UdSdU);
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////////////////////////////////////
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// Modify the gauge field a little
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////////////////////////////////////
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RealD dt = 0.0001;
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LatticeColourMatrix mommu(&Grid);
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LatticeColourMatrix forcemu(&Grid);
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LatticeGaugeField mom(&Grid);
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LatticeGaugeField Uprime(&Grid);
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for(int mu=0;mu<Nd;mu++){
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SU3::GaussianLieAlgebraMatrix(pRNG, mommu); // Traceless antihermitian momentum; gaussian in lie alg
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PokeIndex<LorentzIndex>(mom,mommu,mu);
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// fourth order exponential approx
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parallel_for(auto i=mom.begin();i<mom.end();i++){ // exp(pmu dt) * Umu
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Uprime[i](mu) = U[i](mu) + mom[i](mu)*U[i](mu)*dt ;
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}
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}
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ComplexD Sprime = Action.S(Uprime);
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//////////////////////////////////////////////
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// Use derivative to estimate dS
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//////////////////////////////////////////////
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LatticeComplex dS(&Grid); dS = zero;
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for(int mu=0;mu<Nd;mu++){
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auto UdSdUmu = PeekIndex<LorentzIndex>(UdSdU,mu);
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mommu = PeekIndex<LorentzIndex>(mom,mu);
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// Update gauge action density
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// U = exp(p dt) U
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// dU/dt = p U
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// so dSdt = trace( dUdt dSdU) = trace( p UdSdUmu )
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dS = dS - trace(mommu*UdSdUmu)*dt*2.0;
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}
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Complex dSpred = sum(dS);
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std::cout << GridLogMessage << " S "<<S<<std::endl;
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std::cout << GridLogMessage << " Sprime "<<Sprime<<std::endl;
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std::cout << GridLogMessage << "dS "<<Sprime-S<<std::endl;
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std::cout << GridLogMessage << "pred dS "<< dSpred <<std::endl;
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std::cout<< GridLogMessage << "Done" <<std::endl;
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Grid_finalize();
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}
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