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#ifndef vtkm_worklet_cosmotools_compute_potential_nxn_h
#define vtkm_worklet_cosmotools_compute_potential_nxn_h

#include <vtkm/worklet/WorkletMapField.h>

namespace vtkm
{
namespace worklet
{
namespace cosmotools
{

// Worklet for computing the potential for a particle in one halo
template <typename T>
class ComputePotentialNxN : public vtkm::worklet::WorkletMapField
{
public:
  struct TagType : vtkm::ListTagBase<T>
  {
  };

  using ControlSignature = void(FieldIn<IdType> partId,       // (input) particle Id
                                WholeArrayIn<TagType> xLoc,   // (input) x location in domain
                                WholeArrayIn<TagType> yLoc,   // (input) y location in domain
                                WholeArrayIn<TagType> zLoc,   // (input) z location in domain
                                FieldOut<TagType> potential); // (output) bin ID
  using ExecutionSignature = _5(_1, _2, _3, _4);
  using InputDomain = _1;

  vtkm::Id nParticles; // Number of particles in halo
  T mass;              // Particle mass

  // Constructor
  VTKM_EXEC_CONT
  ComputePotentialNxN(vtkm::Id N, T Mass)
    : nParticles(N)
    , mass(Mass)
  {
  }

  template <typename InFieldPortalType>
  VTKM_EXEC T operator()(const vtkm::Id& i,
                         const InFieldPortalType& xLoc,
                         const InFieldPortalType& yLoc,
                         const InFieldPortalType& zLoc) const
  {
    T potential = 0.0f;
    for (vtkm::Id j = 0; j < nParticles; j++)
    {
      T xDist = xLoc.Get(i) - xLoc.Get(j);
      T yDist = yLoc.Get(i) - yLoc.Get(j);
      T zDist = zLoc.Get(i) - zLoc.Get(j);
      T r = vtkm::Sqrt((xDist * xDist) + (yDist * yDist) + (zDist * zDist));
      if ((i != j) && (fabs(r) > 0.00000000001f))
      {
        potential -= mass / r;
      }
    }
    return potential;
  }
}; // ComputePotentialNxN
}
}
}

#endif
