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Grid/lib/qcd/utils/SUn.h

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/*************************************************************************************
Grid physics library, www.github.com/paboyle/Grid
Source file: ./lib/qcd/utils/SUn.h
Copyright (C) 2015
Author: Azusa Yamaguchi <ayamaguc@staffmail.ed.ac.uk>
Author: Peter Boyle <paboyle@ph.ed.ac.uk>
Author: neo <cossu@post.kek.jp>
Author: paboyle <paboyle@ph.ed.ac.uk>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
See the full license in the file "LICENSE" in the top level distribution directory
*************************************************************************************/
/* END LEGAL */
#ifndef QCD_UTIL_SUN_H
#define QCD_UTIL_SUN_H
namespace Grid {
namespace QCD {
template<int ncolour>
class SU {
public:
static int generators(void) { return ncolour*ncolour-1; }
static int su2subgroups(void) { return (ncolour*(ncolour-1))/2; }
template<typename vtype> using iSUnMatrix = iScalar<iScalar<iMatrix<vtype, ncolour> > > ;
template<typename vtype> using iSU2Matrix = iScalar<iScalar<iMatrix<vtype, 2> > > ;
//////////////////////////////////////////////////////////////////////////////////////////////////
// Types can be accessed as SU<2>::Matrix , SU<2>::vSUnMatrix, SU<2>::LatticeMatrix etc...
//////////////////////////////////////////////////////////////////////////////////////////////////
typedef iSUnMatrix<Complex> Matrix;
typedef iSUnMatrix<ComplexF> MatrixF;
typedef iSUnMatrix<ComplexD> MatrixD;
typedef iSUnMatrix<vComplex> vMatrix;
typedef iSUnMatrix<vComplexF> vMatrixF;
typedef iSUnMatrix<vComplexD> vMatrixD;
typedef Lattice<vMatrix> LatticeMatrix;
typedef Lattice<vMatrixF> LatticeMatrixF;
typedef Lattice<vMatrixD> LatticeMatrixD;
typedef iSU2Matrix<Complex> SU2Matrix;
typedef iSU2Matrix<ComplexF> SU2MatrixF;
typedef iSU2Matrix<ComplexD> SU2MatrixD;
typedef iSU2Matrix<vComplex> vSU2Matrix;
typedef iSU2Matrix<vComplexF> vSU2MatrixF;
typedef iSU2Matrix<vComplexD> vSU2MatrixD;
typedef Lattice<vSU2Matrix> LatticeSU2Matrix;
typedef Lattice<vSU2MatrixF> LatticeSU2MatrixF;
typedef Lattice<vSU2MatrixD> LatticeSU2MatrixD;
////////////////////////////////////////////////////////////////////////
// There are N^2-1 generators for SU(N).
//
// We take a traceless hermitian generator basis as follows
//
// * Normalisation: trace ta tb = 1/2 delta_ab
//
// * Off diagonal
// - pairs of rows i1,i2 behaving like pauli matrices signma_x, sigma_y
//
// - there are (Nc-1-i1) slots for i2 on each row [ x 0 x ]
// direct count off each row
//
// - Sum of all pairs is Nc(Nc-1)/2: proof arithmetic series
//
// (Nc-1) + (Nc-2)+... 1 ==> Nc*(Nc-1)/2
// 1+ 2+ + + Nc-1
//
// - There are 2 x Nc (Nc-1)/ 2 of these = Nc^2 - Nc
//
// - We enumerate the row-col pairs.
// - for each row col pair there is a (sigma_x) and a (sigma_y) like generator
//
//
// t^a_ij = { in 0.. Nc(Nc-1)/2 -1} => delta_{i,i1} delta_{j,i2} + delta_{i,i1} delta_{j,i2}
// t^a_ij = { in Nc(Nc-1)/2 ... Nc^(Nc-1) -1} => i delta_{i,i1} delta_{j,i2} - i delta_{i,i1} delta_{j,i2}
//
// * Diagonal; must be traceless and normalised
// - Sequence is
// N (1,-1,0,0...)
// N (1, 1,-2,0...)
// N (1, 1, 1,-3,0...)
// N (1, 1, 1, 1,-4,0...)
//
// where 1/2 = N^2 (1+.. m^2)etc.... for the m-th diagonal generator
// NB this gives the famous SU3 result for su2 index 8
//
// N= sqrt(1/2 . 1/6 ) = 1/2 . 1/sqrt(3)
//
// ( 1 )
// ( 1 ) / sqrt(3) /2 = 1/2 lambda_8
// ( -2)
////////////////////////////////////////////////////////////////////////
template<class cplx>
static void generator(int lieIndex,iSUnMatrix<cplx> &ta){
// map lie index to which type of generator
int diagIndex;
int su2Index;
int sigxy;
int NNm1 = ncolour*(ncolour-1);
if ( lieIndex>= NNm1 ) {
diagIndex = lieIndex -NNm1;
generatorDiagonal(diagIndex,ta);
return;
}
sigxy = lieIndex&0x1;
su2Index= lieIndex>>1;
if ( sigxy ) generatorSigmaY(su2Index,ta);
else generatorSigmaX(su2Index,ta);
}
template<class cplx>
static void generatorSigmaX(int su2Index,iSUnMatrix<cplx> &ta){
ta=zero;
int i1,i2;
su2SubGroupIndex(i1,i2,su2Index);
ta()()(i1,i2)=1.0;
ta()()(i2,i1)=1.0;
ta= ta *0.5;
}
template<class cplx>
static void generatorSigmaY(int su2Index,iSUnMatrix<cplx> &ta){
ta=zero;
cplx i(0.0,1.0);
int i1,i2;
su2SubGroupIndex(i1,i2,su2Index);
ta()()(i1,i2)=-i;
ta()()(i2,i1)= i;
ta= ta *0.5;
}
template<class cplx>
static void generatorDiagonal(int diagIndex,iSUnMatrix<cplx> &ta){
ta=zero;
int trsq=0;
int last=diagIndex+1;
for(int i=0;i<=diagIndex;i++){
ta()()(i,i) = 1.0;
trsq++;
}
ta()()(last,last) = -last;
trsq+=last*last;
RealD nrm = 1.0/std::sqrt(2.0*trsq);
ta = ta *nrm;
}
////////////////////////////////////////////////////////////////////////
// Map a su2 subgroup number to the pair of rows that are non zero
////////////////////////////////////////////////////////////////////////
static void su2SubGroupIndex(int &i1,int &i2,int su2_index){
assert( (su2_index>=0) && (su2_index< (ncolour*(ncolour-1))/2) );
int spare=su2_index;
for(i1=0;spare >= (ncolour-1-i1);i1++ ){
spare = spare - (ncolour-1-i1); // remove the Nc-1-i1 terms
}
i2=i1+1+spare;
}
//////////////////////////////////////////////////////////////////////////////////////////
// Pull out a subgroup and project on to real coeffs x pauli basis
//////////////////////////////////////////////////////////////////////////////////////////
template<class vcplx>
static void su2Extract( Lattice<iSinglet<vcplx> > &Determinant,
Lattice<iSU2Matrix<vcplx> > &subgroup,
const Lattice<iSUnMatrix<vcplx> > &source,
int su2_index)
{
GridBase *grid(source._grid);
conformable(subgroup,source);
conformable(subgroup,Determinant);
int i0,i1;
su2SubGroupIndex(i0,i1,su2_index);
PARALLEL_FOR_LOOP
for(int ss=0;ss<grid->oSites();ss++){
subgroup._odata[ss]()()(0,0) = source._odata[ss]()()(i0,i0);
subgroup._odata[ss]()()(0,1) = source._odata[ss]()()(i0,i1);
subgroup._odata[ss]()()(1,0) = source._odata[ss]()()(i1,i0);
subgroup._odata[ss]()()(1,1) = source._odata[ss]()()(i1,i1);
iSU2Matrix<vcplx> Sigma = subgroup._odata[ss];
Sigma = Sigma-adj(Sigma)+trace(adj(Sigma));
subgroup._odata[ss] = Sigma;
// this should be purely real
Determinant._odata[ss] = Sigma()()(0,0)*Sigma()()(1,1)
- Sigma()()(0,1)*Sigma()()(1,0);
}
}
//////////////////////////////////////////////////////////////////////////////////////////
// Set matrix to one and insert a pauli subgroup
//////////////////////////////////////////////////////////////////////////////////////////
template<class vcplx>
static void su2Insert( const Lattice<iSU2Matrix<vcplx> > &subgroup,
Lattice<iSUnMatrix<vcplx> > &dest,
int su2_index)
{
GridBase *grid(dest._grid);
conformable(subgroup,dest);
int i0,i1;
su2SubGroupIndex(i0,i1,su2_index);
dest = 1.0; // start out with identity
PARALLEL_FOR_LOOP
for(int ss=0;ss<grid->oSites();ss++){
dest._odata[ss]()()(i0,i0) = subgroup._odata[ss]()()(0,0);
dest._odata[ss]()()(i0,i1) = subgroup._odata[ss]()()(0,1);
dest._odata[ss]()()(i1,i0) = subgroup._odata[ss]()()(1,0);
dest._odata[ss]()()(i1,i1) = subgroup._odata[ss]()()(1,1);
}
}
///////////////////////////////////////////////
// Generate e^{ Re Tr Staple Link} dlink
//
// *** Note Staple should be appropriate linear compbination between all staples.
// *** If already by beta pass coefficient 1.0.
// *** This routine applies the additional 1/Nc factor that comes after trace in action.
//
///////////////////////////////////////////////
static void SubGroupHeatBath( GridSerialRNG &sRNG,
GridParallelRNG &pRNG,
RealD beta,//coeff multiplying staple in action (with no 1/Nc)
LatticeMatrix &link,
const LatticeMatrix &barestaple, // multiplied by action coeffs so th
int su2_subgroup,
int nheatbath,
LatticeInteger &wheremask)
{
GridBase *grid = link._grid;
int ntrials=0;
int nfails=0;
const RealD twopi=2.0*M_PI;
LatticeMatrix staple(grid);
staple = barestaple * (beta/ncolour);
LatticeMatrix V(grid); V = link*staple;
// Subgroup manipulation in the lie algebra space
LatticeSU2Matrix u(grid); // Kennedy pendleton "u" real projected normalised Sigma
LatticeSU2Matrix uinv(grid);
LatticeSU2Matrix ua(grid); // a in pauli form
LatticeSU2Matrix b(grid); // rotated matrix after hb
// Some handy constant fields
LatticeComplex ones (grid); ones = 1.0;
LatticeComplex zeros(grid); zeros=zero;
LatticeReal rones (grid); rones = 1.0;
LatticeReal rzeros(grid); rzeros=zero;
LatticeComplex udet(grid); // determinant of real(staple)
LatticeInteger mask_true (grid); mask_true = 1;
LatticeInteger mask_false(grid); mask_false= 0;
/*
PLB 156 P393 (1985) (Kennedy and Pendleton)
Note: absorb "beta" into the def of sigma compared to KP paper; staple
passed to this routine has "beta" already multiplied in
Action linear in links h and of form:
beta S = beta Sum_p (1 - 1/Nc Re Tr Plaq )
Writing Sigma = 1/Nc (beta Sigma') where sum over staples is "Sigma' "
beta S = const - beta/Nc Re Tr h Sigma'
= const - Re Tr h Sigma
Decompose h and Sigma into (1, sigma_j) ; h_i real, h^2=1, Sigma_i complex arbitrary.
Tr h Sigma = h_i Sigma_j Tr (sigma_i sigma_j) = h_i Sigma_j 2 delta_ij
Re Tr h Sigma = 2 h_j Re Sigma_j
Normalised re Sigma_j = xi u_j
With u_j a unit vector and U can be in SU(2);
Re Tr h Sigma = 2 h_j Re Sigma_j = 2 xi (h.u)
4xi^2 = Det [ Sig - Sig^dag + 1 Tr Sigdag]
u = 1/2xi [ Sig - Sig^dag + 1 Tr Sigdag]
xi = sqrt(Det)/2;
Write a= u h in SU(2); a has pauli decomp a_j;
Note: Product b' xi is unvariant because scaling Sigma leaves
normalised vector "u" fixed; Can rescale Sigma so b' = 1.
*/
////////////////////////////////////////////////////////
// Real part of Pauli decomposition
// Note a subgroup can project to zero in cold start
////////////////////////////////////////////////////////
su2Extract(udet,u,V,su2_subgroup);
//////////////////////////////////////////////////////
// Normalising this vector if possible; else identity
//////////////////////////////////////////////////////
LatticeComplex xi(grid);
LatticeSU2Matrix lident(grid);
SU2Matrix ident = Complex(1.0);
SU2Matrix pauli1; SU<2>::generator(0,pauli1);
SU2Matrix pauli2; SU<2>::generator(1,pauli2);
SU2Matrix pauli3; SU<2>::generator(2,pauli3);
pauli1 = timesI(pauli1)*2.0;
pauli2 = timesI(pauli2)*2.0;
pauli3 = timesI(pauli3)*2.0;
LatticeComplex cone(grid);
LatticeReal adet(grid);
adet = abs(toReal(udet));
lident=Complex(1.0);
cone =Complex(1.0);
Real machine_epsilon=1.0e-7;
u = where(adet>machine_epsilon,u,lident);
udet= where(adet>machine_epsilon,udet,cone);
xi = 0.5*sqrt(udet); //4xi^2 = Det [ Sig - Sig^dag + 1 Tr Sigdag]
u = 0.5*u*pow(xi,-1.0); // u = 1/2xi [ Sig - Sig^dag + 1 Tr Sigdag]
// Debug test for sanity
uinv=adj(u);
b=u*uinv-1.0;
assert(norm2(b)<1.0e-4);
/*
Measure: Haar measure dh has d^4a delta(1-|a^2|)
In polars:
da = da0 r^2 sin theta dr dtheta dphi delta( 1 - r^2 -a0^2)
= da0 r^2 sin theta dr dtheta dphi delta( (sqrt(1-a0^) - r)(sqrt(1-a0^) + r) )
= da0 r/2 sin theta dr dtheta dphi delta( (sqrt(1-a0^) - r) )
Action factor Q(h) dh = e^-S[h] dh = e^{ xi Tr uh} dh // beta enters through xi
= e^{2 xi (h.u)} dh
= e^{2 xi h0u0}.e^{2 xi h1u1}.e^{2 xi h2u2}.e^{2 xi h3u3} dh
Therefore for each site, take xi for that site
i) generate |a0|<1 with dist
(1-a0^2)^0.5 e^{2 xi a0 } da0
Take alpha = 2 xi = 2 xi [ recall 2 beta/Nc unmod staple norm]; hence 2.0/Nc factor in Chroma ]
A. Generate two uniformly distributed pseudo-random numbers R and R', R'', R''' in the unit interval;
B. Set X = -(ln R)/alpha, X' =-(ln R')/alpha;
C. Set C = cos^2(2pi R"), with R" another uniform random number in [0,1] ;
D. Set A = XC;
E. Let d = X'+A;
F. If R'''^2 :> 1 - 0.5 d, go back to A;
G. Set a0 = 1 - d;
Note that in step D setting B ~ X - A and using B in place of A in step E will generate a second independent a 0 value.
*/
/////////////////////////////////////////////////////////
// count the number of sites by picking "1"'s out of hat
/////////////////////////////////////////////////////////
Integer hit=0;
LatticeReal rtmp(grid);
rtmp=where(wheremask,rones,rzeros);
RealD numSites = sum(rtmp);
RealD numAccepted;
LatticeInteger Accepted(grid); Accepted = zero;
LatticeInteger newlyAccepted(grid);
std::vector<LatticeReal> xr(4,grid);
std::vector<LatticeReal> a(4,grid);
LatticeReal d(grid); d=zero;
LatticeReal alpha(grid);
// std::cout<<GridLogMessage<<"xi "<<xi <<std::endl;
alpha = toReal(2.0*xi);
do {
// A. Generate two uniformly distributed pseudo-random numbers R and R', R'', R''' in the unit interval;
random(pRNG,xr[0]);
random(pRNG,xr[1]);
random(pRNG,xr[2]);
random(pRNG,xr[3]);
// B. Set X = - ln R/alpha, X' = -ln R'/alpha
xr[1] = -log(xr[1])/alpha;
xr[2] = -log(xr[2])/alpha;
// C. Set C = cos^2(2piR'')
xr[3] = cos(xr[3]*twopi);
xr[3] = xr[3]*xr[3];
LatticeReal xrsq(grid);
//D. Set A = XC;
//E. Let d = X'+A;
xrsq = xr[2]+xr[1]*xr[3];
d = where(Accepted,d,xr[2]+xr[1]*xr[3]);
//F. If R'''^2 :> 1 - 0.5 d, go back to A;
LatticeReal thresh(grid); thresh = 1.0-d*0.5;
xrsq = xr[0]*xr[0];
LatticeInteger ione(grid); ione = 1;
LatticeInteger izero(grid); izero=zero;
newlyAccepted = where ( xrsq < thresh,ione,izero);
Accepted = where ( newlyAccepted, newlyAccepted,Accepted);
Accepted = where ( wheremask, Accepted,izero);
// FIXME need an iSum for integer to avoid overload on return type??
rtmp=where(Accepted,rones,rzeros);
numAccepted = sum(rtmp);
hit++;
} while ( (numAccepted < numSites) && ( hit < nheatbath) );
// G. Set a0 = 1 - d;
a[0]=zero;
a[0]=where(wheremask,1.0-d,a[0]);
//////////////////////////////////////////
// ii) generate a_i uniform on two sphere radius (1-a0^2)^0.5
//////////////////////////////////////////
LatticeReal a123mag(grid);
a123mag = sqrt(abs(1.0-a[0]*a[0]));
LatticeReal cos_theta (grid);
LatticeReal sin_theta (grid);
LatticeReal phi (grid);
random(pRNG,phi); phi = phi * twopi; // uniform in [0,2pi]
random(pRNG,cos_theta); cos_theta=(cos_theta*2.0)-1.0; // uniform in [-1,1]
sin_theta = sqrt(abs(1.0-cos_theta*cos_theta));
a[1] = a123mag * sin_theta * cos(phi);
a[2] = a123mag * sin_theta * sin(phi);
a[3] = a123mag * cos_theta;
ua = toComplex(a[0])*ident
+ toComplex(a[1])*pauli1
+ toComplex(a[2])*pauli2
+ toComplex(a[3])*pauli3;
b = 1.0;
b = where(wheremask,uinv*ua,b);
su2Insert(b,V,su2_subgroup);
//mask the assignment back based on Accptance
link = where(Accepted,V * link,link);
//////////////////////////////
// Debug Checks
// SU2 check
LatticeSU2Matrix check(grid); // rotated matrix after hb
u = zero;
check = ua * adj(ua) - 1.0;
check = where(Accepted,check,u);
assert(norm2(check)<1.0e-4);
check = b*adj(b)-1.0;
check = where(Accepted,check,u);
assert(norm2(check)<1.0e-4);
LatticeMatrix Vcheck(grid);
Vcheck = zero;
Vcheck = where(Accepted,V*adj(V) - 1.0,Vcheck);
// std::cout<<GridLogMessage << "SU3 check " <<norm2(Vcheck)<<std::endl;
assert(norm2(Vcheck)<1.0e-4);
// Verify the link stays in SU(3)
// std::cout<<GridLogMessage <<"Checking the modified link"<<std::endl;
Vcheck = link*adj(link) - 1.0;
assert(norm2(Vcheck)<1.0e-4);
/////////////////////////////////
}
static void printGenerators(void)
{
for(int gen=0;gen<generators();gen++){
Matrix ta;
generator(gen,ta);
std::cout<<GridLogMessage<< "Nc = "<<ncolour<<" t_"<<gen<<std::endl;
std::cout<<GridLogMessage<<ta<<std::endl;
}
}
static void testGenerators(void){
Matrix ta;
Matrix tb;
std::cout<<GridLogMessage<<"Checking trace ta tb is 0.5 delta_ab"<<std::endl;
for(int a=0;a<generators();a++){
for(int b=0;b<generators();b++){
generator(a,ta);
generator(b,tb);
Complex tr =TensorRemove(trace(ta*tb));
std::cout<<GridLogMessage<<tr<<" ";
if(a==b) assert(abs(tr-Complex(0.5))<1.0e-6);
if(a!=b) assert(abs(tr)<1.0e-6);
}
std::cout<<GridLogMessage<<std::endl;
}
std::cout<<GridLogMessage<<"Checking hermitian"<<std::endl;
for(int a=0;a<generators();a++){
generator(a,ta);
std::cout<<GridLogMessage<<a<<" ";
assert(norm2(ta-adj(ta))<1.0e-6);
}
std::cout<<GridLogMessage<<std::endl;
std::cout<<GridLogMessage<<"Checking traceless"<<std::endl;
for(int a=0;a<generators();a++){
generator(a,ta);
Complex tr =TensorRemove(trace(ta));
std::cout<<GridLogMessage<<a<<" ";
assert(abs(tr)<1.0e-6);
}
std::cout<<GridLogMessage<<std::endl;
}
// reunitarise??
static void LieRandomize(GridParallelRNG &pRNG,LatticeMatrix &out,double scale=1.0){
GridBase *grid = out._grid;
LatticeComplex ca (grid);
LatticeMatrix lie(grid);
LatticeMatrix la (grid);
Complex ci(0.0,scale);
Complex cone(1.0,0.0);
Matrix ta;
lie=zero;
for(int a=0;a<generators();a++){
random(pRNG,ca);
ca = (ca+conjugate(ca))*0.5;
ca = ca - 0.5;
generator(a,ta);
la=ci*ca*ta;
lie = lie+la; // e^{i la ta}
}
taExp(lie,out);
}
static void GaussianLieAlgebraMatrix(GridParallelRNG &pRNG,LatticeMatrix &out,double scale=1.0){
GridBase *grid = out._grid;
LatticeReal ca (grid);
LatticeMatrix la (grid);
Complex ci(0.0,scale);
Matrix ta;
out=zero;
for(int a=0;a<generators();a++){
gaussian(pRNG,ca);
generator(a,ta);
la=toComplex(ca)*ci*ta;
out += la;
}
}
static void HotConfiguration(GridParallelRNG &pRNG,LatticeGaugeField &out){
LatticeMatrix Umu(out._grid);
for(int mu=0;mu<Nd;mu++){
LieRandomize(pRNG,Umu,1.0);
PokeIndex<LorentzIndex>(out,Umu,mu);
}
}
static void TepidConfiguration(GridParallelRNG &pRNG,LatticeGaugeField &out){
LatticeMatrix Umu(out._grid);
for(int mu=0;mu<Nd;mu++){
LieRandomize(pRNG,Umu,0.01);
pokeLorentz(out,Umu,mu);
}
}
static void ColdConfiguration(GridParallelRNG &pRNG,LatticeGaugeField &out){
LatticeMatrix Umu(out._grid);
Umu=1.0;
for(int mu=0;mu<Nd;mu++){
pokeLorentz(out,Umu,mu);
}
}
static void taProj( const LatticeMatrix &in, LatticeMatrix &out){
out = Ta(in);
}
static void taExp( const LatticeMatrix &x, LatticeMatrix &ex){
LatticeMatrix xn(x._grid);
RealD nfac = 1.0;
xn = x;
ex =xn+Complex(1.0); // 1+x
// Do a 12th order exponentiation
for(int i=2; i <= 12; ++i)
{
nfac = nfac/RealD(i); //1/2, 1/2.3 ...
xn = xn * x; // x2, x3,x4....
ex = ex+ xn*nfac;// x2/2!, x3/3!....
}
}
};
typedef SU<2> SU2;
typedef SU<3> SU3;
typedef SU<4> SU4;
typedef SU<5> SU5;
}
}
#endif
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