weak_field.cc

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/*! \file
 *  \brief Construct a weak field
 */
 
#include "chromabase.h"
#include "util/gauge/weak_field.h"
#include "util/gauge/sunfill.h"
 
namespace Chroma
{
 
  //! Construct a weak field
  /*!
   * \ingroup gauge
   *
   * Make a gauge field close to free field - e.g., small fluctations
   *
   * Arguments:
   *
   *  \param u          Gauge field                   (Modify)
   */
  void weakField(multi1d<LatticeColorMatrix>& u)
  {
    START_CODE();
 
    u.resize(Nd);
 
    Real amp = 0.02 * twopi;
    LatticeReal theta;
    LatticeColorMatrix s1, s2;
    multi1d<LatticeReal> a(4);
    Real fact = 1.0 / sqrt(2.0);
 
    for(int mu = 0; mu < Nd; mu++)
    {
      u[mu] = 1.0;
 
      for(int su2_index = 0; su2_index < Nc*(Nc-1)/2; su2_index++)
      {
        // Embed a SU(2) within SU(N)
        random(theta);
        theta *= amp;
        a[0] = fact*cos(theta);
        a[1] = fact*sin(theta);
 
        random(theta);
        theta *= amp;
        a[2] = fact*cos(theta);
        a[3] = fact*sin(theta);
 
        s1 = 1.0;
        sunFill(s1, a, su2_index, all);
 
        // Mix up the indices by multiplying - still unitary
        s2 = u[mu] * s1;
        u[mu] = s2;
      }
    }
 
    END_CODE();
  }
}