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#ifndef vtkm_worklet_cosmotools_compute_potential_h
#define vtkm_worklet_cosmotools_compute_potential_h

#include <vtkm/worklet/WorkletMapField.h>

namespace vtkm
{
namespace worklet
{
namespace cosmotools
{

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

  using ControlSignature =
    void(FieldIn<IdType> index,                // (input) particle Id
         WholeArrayIn<IdType> partId,          // (input) first particle in halo
         WholeArrayIn<TagType> xLoc,           // (input) x location in domain
         WholeArrayIn<TagType> yLoc,           // (input) y location in domain
         WholeArrayIn<TagType> zLoc,           // (input) z location in domain
         WholeArrayIn<IdType> firstParticleId, // (input) first particle in halo
         WholeArrayIn<IdType> lastParticleId,  // (input) last particle in halo
         FieldOut<TagType> potential);         // (output) bin ID
  using ExecutionSignature = _8(_1, _2, _3, _4, _5, _6, _7);
  using InputDomain = _1;

  T mass;

  // Constructor
  VTKM_EXEC_CONT
  ComputePotential(T Mass)
    : mass(Mass)
  {
  }

  template <typename InFieldPortalType, typename InIdPortalType, typename PermutePortalType>
  VTKM_EXEC T operator()(const vtkm::Id& i,
                         const InIdPortalType& partId,
                         const InFieldPortalType& xLoc,
                         const InFieldPortalType& yLoc,
                         const InFieldPortalType& zLoc,
                         const InIdPortalType& firstParticleId,
                         const PermutePortalType& lastParticleId) const
  {
    // Worklet index is into array of particle ids sorted by bin
    // Current particle and other particles retrieved from partId array
    vtkm::Id iId = partId.Get(i);
    T potential = 0.0f;

    // first and last particle are arranged by sorted bin id so they match index and not the partId
    for (vtkm::Id j = firstParticleId.Get(i); j <= lastParticleId.Get(i); j++)
    {
      vtkm::Id jId = partId.Get(j);
      T xDist = xLoc.Get(iId) - xLoc.Get(jId);
      T yDist = yLoc.Get(iId) - yLoc.Get(jId);
      T zDist = zLoc.Get(iId) - zLoc.Get(jId);
      T r = vtkm::Sqrt((xDist * xDist) + (yDist * yDist) + (zDist * zDist));
      if ((i != j) && (fabs(r) > 0.00000000001f))
        potential -= mass / r;
    }
    return potential;
  }
}; // ComputePotential
}
}
}

#endif
