Got the NERSC IO working and fixed a bug in cshift.

tests/Grid_nersc_io.cc

@@ -0,0 +1,62 @@
+#include <Grid.h>
+#include <parallelIO/GridNerscIO.h>
+
+using namespace std;
+using namespace Grid;
+using namespace Grid::QCD;
+
+
+int main (int argc, char ** argv)
+{
+  Grid_init(&argc,&argv);
+
+  std::vector<int> simd_layout({1,1,2,2});
+  std::vector<int> mpi_layout ({2,1,1,2});
+  std::vector<int> latt_size  ({16,16,16,32});
+    
+  GridCartesian     Fine(latt_size,simd_layout,mpi_layout);
+  GridRNG           FineRNG(&Fine);
+  LatticeGaugeField Umu(&Fine);
+
+  std::vector<LatticeColourMatrix> U(4,&Fine);
+  
+  NerscField header;
+  
+  std::string file("./ckpoint_lat.4000");
+  readNerscConfiguration(Umu,header,file);
+
+  for(int mu=0;mu<Nd;mu++){
+    U[mu] = peekIndex<3>(Umu,mu);
+  }
+
+  // Painful ; fix syntactical niceness
+  LatticeComplex LinkTrace(&Fine);
+  LinkTrace=zero;
+  for(int mu=0;mu<Nd;mu++){
+    LinkTrace = LinkTrace + trace(U[mu]);
+  }
+
+  // (1+2+3)=6 = N(N-1)/2 terms
+  LatticeComplex Plaq(&Fine);
+  Plaq = zero;
+  for(int mu=1;mu<Nd;mu++){
+    for(int nu=0;nu<mu;nu++){
+      Plaq = Plaq + trace(U[mu]*Cshift(U[nu],mu,1)*adj(Cshift(U[mu],nu,1))*adj(U[nu]));
+    }
+  }
+
+
+  double vol = Fine.gSites();
+
+  Complex PlaqScale(1.0/vol/6.0/3.0);
+  TComplex Tp = sum(Plaq);
+  Complex p  = TensorRemove(Tp);
+  std::cout << "calculated plaquettes " <<p*PlaqScale<<std::endl;
+
+  Complex LinkTraceScale(1.0/vol/4.0/3.0);
+  TComplex Tl = sum(LinkTrace);
+  Complex l  = TensorRemove(Tl);
+  std::cout << "calculated link trace " <<l*LinkTraceScale<<std::endl;
+
+  Grid_finalize();
+}