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/* Copyright 2019-2020 Andrew Myers, Yinjian Zhao
*
* This file is part of WarpX.
*
* License: BSD-3-Clause-LBNL
*/
#ifndef WARPX_PARTICLES_COLLISION_COMPUTE_TEMPERATURE_H_
#define WARPX_PARTICLES_COLLISION_COMPUTE_TEMPERATURE_H_
#include "Utils/WarpXConst.H"
template <typename T_index, typename T_R>
AMREX_GPU_HOST_DEVICE
T_R ComputeTemperature (
T_index const Is, T_index const Ie, T_index const *I,
T_R const *ux, T_R const *uy, T_R const *uz, T_R const m )
{
T_R constexpr inv_c2 = T_R(1.0) / ( PhysConst::c * PhysConst::c );
int N = Ie - Is;
if ( N == 0 ) { return T_R(0.0); }
T_R vx = T_R(0.0); T_R vy = T_R(0.0);
T_R vz = T_R(0.0); T_R vs = T_R(0.0);
T_R gm = T_R(0.0); T_R us = T_R(0.0);
for (int i = Is; i < static_cast<int>(Ie); ++i)
{
us = ( ux[ I[i] ] * ux[ I[i] ] +
uy[ I[i] ] * uy[ I[i] ] +
uz[ I[i] ] * uz[ I[i] ] );
gm = std::sqrt( T_R(1.0) + us*inv_c2 );
vx += ux[ I[i] ] / gm;
vy += uy[ I[i] ] / gm;
vz += uz[ I[i] ] / gm;
vs += us / gm / gm;
}
vx = vx / N; vy = vy / N;
vz = vz / N; vs = vs / N;
return m/T_R(3.0)*(vs-(vx*vx+vy*vy+vz*vz));
}
#endif // WARPX_PARTICLES_COLLISION_COMPUTE_TEMPERATURE_H_
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