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/* Copyright 2019 David Grote, Luca Fedeli, Maxence Thevenet
* Remi Lehe, Weiqun Zhang
*
* This file is part of WarpX.
*
* License: BSD-3-Clause-LBNL
*/
#ifndef WARPX_PARTICLES_PUSHER_UPDATEPOSITIONPHOTON_H_
#define WARPX_PARTICLES_PUSHER_UPDATEPOSITIONPHOTON_H_
#include "Utils/WarpXConst.H"
#include <AMReX.H>
#include <AMReX_FArrayBox.H>
#include <AMReX_REAL.H>
/**
* \brief Push the position of a photon particle over one timestep,
* given the value of its momenta `ux`, `uy`, `uz`
*/
AMREX_GPU_HOST_DEVICE AMREX_INLINE
void UpdatePositionPhoton(
amrex::ParticleReal& x, amrex::ParticleReal& y, amrex::ParticleReal& z,
const amrex::ParticleReal ux, const amrex::ParticleReal uy, const amrex::ParticleReal uz,
const amrex::Real dt )
{
using namespace amrex::literals;
// Compute speed of light over inverse of momentum modulus, avoiding a division by zero in the
// case where the photon has exactly zero momentum
const amrex::ParticleReal u_norm = std::sqrt(ux*ux + uy*uy + uz*uz);
const amrex::ParticleReal c_over_umod = (u_norm == 0._prt) ? 0._prt: PhysConst::c/u_norm;
// Update positions over one time step
#if (AMREX_SPACEDIM >= 2)
x += ux * c_over_umod * dt;
#else
amrex::ignore_unused(x);
#endif
#if (defined WARPX_DIM_3D) || (defined WARPX_DIM_RZ) // RZ pushes particles in 3D
y += uy * c_over_umod * dt;
#else
amrex::ignore_unused(y);
#endif
z += uz * c_over_umod * dt;
}
#endif // WARPX_PARTICLES_PUSHER_UPDATEPOSITION_H_
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