/******************************************************************************* * This file is part of SWIFT. * Copyright (c) 2024 Thomas Sandnes (thomas.d.sandnes@durham.ac.uk) * 2024 Jacob Kegerreis (jacob.kegerreis@durham.ac.uk) * 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk) * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU Lesser General Public License as published * by the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with this program. If not, see . * ******************************************************************************/ #ifndef SWIFT_REMIX_HYDRO_IACT_H #define SWIFT_REMIX_HYDRO_IACT_H /** * @file REMIX/hydro_iact.h * @brief REMIX implementation of SPH (Sandnes et al. 2025) */ #include "adiabatic_index.h" #include "const.h" #include "hydro_kernels.h" #include "hydro_parameters.h" #include "hydro_visc_difn.h" #include "math.h" #include "minmax.h" /** * @brief Density interaction between two particles. * * @param r2 Comoving square distance between the two particles. * @param dx Comoving vector separating both particles (pi - pj). * @param hi Comoving smoothing-length of particle i. * @param hj Comoving smoothing-length of particle j. * @param pi First particle. * @param pj Second particle. * @param a Current scale factor. * @param H Current Hubble parameter. */ __attribute__((always_inline)) INLINE static void runner_iact_density( const float r2, const float dx[3], const float hi, const float hj, struct part *restrict pi, struct part *restrict pj, const float a, const float H) { float wi, wj, wi_dx, wj_dx; #ifdef SWIFT_DEBUG_CHECKS if (pi->time_bin >= time_bin_inhibited) error("Inhibited pi in interaction function!"); if (pj->time_bin >= time_bin_inhibited) error("Inhibited pj in interaction function!"); #endif /* Get r */ const float r = sqrtf(r2); /* Get the masses. */ const float mi = pi->mass; const float mj = pj->mass; /* Compute density of pi. */ const float hi_inv = 1.f / hi; const float ui = r * hi_inv; kernel_deval(ui, &wi, &wi_dx); pi->rho += mj * wi; pi->density.rho_dh -= mj * (hydro_dimension * wi + ui * wi_dx); pi->density.wcount += wi; pi->density.wcount_dh -= (hydro_dimension * wi + ui * wi_dx); /* Compute density of pj. */ const float hj_inv = 1.f / hj; const float uj = r * hj_inv; kernel_deval(uj, &wj, &wj_dx); pj->rho += mi * wj; pj->density.rho_dh -= mi * (hydro_dimension * wj + uj * wj_dx); pj->density.wcount += wj; pj->density.wcount_dh -= (hydro_dimension * wj + uj * wj_dx); hydro_runner_iact_density_extra_kernel(pi, pj, dx, wi, wj, wi_dx, wj_dx); } /** * @brief Density interaction between two particles (non-symmetric). * * @param r2 Comoving square distance between the two particles. * @param dx Comoving vector separating both particles (pi - pj). * @param hi Comoving smoothing-length of particle i. * @param hj Comoving smoothing-length of particle j. * @param pi First particle. * @param pj Second particle (not updated). * @param a Current scale factor. * @param H Current Hubble parameter. */ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_density( const float r2, const float dx[3], const float hi, const float hj, struct part *restrict pi, const struct part *restrict pj, const float a, const float H) { float wi, wi_dx; #ifdef SWIFT_DEBUG_CHECKS if (pi->time_bin >= time_bin_inhibited) error("Inhibited pi in interaction function!"); if (pj->time_bin >= time_bin_inhibited) error("Inhibited pj in interaction function!"); #endif /* Get the masses. */ const float mj = pj->mass; /* Get r. */ const float r = sqrtf(r2); const float h_inv = 1.f / hi; const float ui = r * h_inv; kernel_deval(ui, &wi, &wi_dx); pi->rho += mj * wi; pi->density.rho_dh -= mj * (hydro_dimension * wi + ui * wi_dx); pi->density.wcount += wi; pi->density.wcount_dh -= (hydro_dimension * wi + ui * wi_dx); hydro_runner_iact_nonsym_density_extra_kernel(pi, pj, dx, wi, wi_dx); } /** * @brief Calculate the gradient interaction between particle i and particle j * * This method wraps around hydro_gradients_collect, which can be an empty * method, in which case no gradients are used. * * @param r2 Comoving square distance between the two particles. * @param dx Comoving vector separating both particles (pi - pj). * @param hi Comoving smoothing-length of particle i. * @param hj Comoving smoothing-length of particle j. * @param pi First particle. * @param pj Second particle. * @param a Current scale factor. * @param H Current Hubble parameter. */ __attribute__((always_inline)) INLINE static void runner_iact_gradient( float r2, const float *dx, float hi, float hj, struct part *restrict pi, struct part *restrict pj, float a, float H) { float wi, wj, wi_dx, wj_dx; /* Get r. */ const float r = sqrtf(r2); /* Compute kernel of pi. */ const float hi_inv = 1.f / hi; const float ui = r * hi_inv; kernel_deval(ui, &wi, &wi_dx); /* Compute kernel of pj. */ const float hj_inv = 1.f / hj; const float uj = r * hj_inv; kernel_deval(uj, &wj, &wj_dx); hydro_runner_iact_gradient_extra_kernel(pi, pj, dx, wi, wj, wi_dx, wj_dx); hydro_runner_iact_gradient_extra_visc_difn(pi, pj, dx, wi, wj, wi_dx, wj_dx); } /** * @brief Calculate the gradient interaction between particle i and particle j: * non-symmetric version * * This method wraps around hydro_gradients_nonsym_collect, which can be an * empty method, in which case no gradients are used. * * @param r2 Comoving square distance between the two particles. * @param dx Comoving vector separating both particles (pi - pj). * @param hi Comoving smoothing-length of particle i. * @param hj Comoving smoothing-length of particle j. * @param pi First particle. * @param pj Second particle (not updated). * @param a Current scale factor. * @param H Current Hubble parameter. */ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_gradient( float r2, const float *dx, float hi, float hj, struct part *restrict pi, struct part *restrict pj, float a, float H) { float wi, wj, wi_dx, wj_dx; /* Get r. */ const float r = sqrtf(r2); /* Compute kernel of pi. */ const float h_inv = 1.f / hi; const float ui = r * h_inv; kernel_deval(ui, &wi, &wi_dx); /* Compute kernel of pj. */ const float hj_inv = 1.f / hj; const float uj = r * hj_inv; kernel_deval(uj, &wj, &wj_dx); hydro_runner_iact_nonsym_gradient_extra_kernel(pi, pj, dx, wi, wj, wi_dx, wj_dx); hydro_runner_iact_nonsym_gradient_extra_visc_difn(pi, pj, dx, wi, wi_dx); } /** * @brief Force interaction between two particles. * * @param r2 Comoving square distance between the two particles. * @param dx Comoving vector separating both particles (pi - pj). * @param hi Comoving smoothing-length of particle i. * @param hj Comoving smoothing-length of particle j. * @param pi First particle. * @param pj Second particle. * @param a Current scale factor. * @param H Current Hubble parameter. */ __attribute__((always_inline)) INLINE static void runner_iact_force( const float r2, const float dx[3], const float hi, const float hj, struct part *restrict pi, struct part *restrict pj, const float a, const float H) { #ifdef SWIFT_DEBUG_CHECKS if (pi->time_bin >= time_bin_inhibited) error("Inhibited pi in interaction function!"); if (pj->time_bin >= time_bin_inhibited) error("Inhibited pj in interaction function!"); #endif /* Get r. */ const float r = sqrtf(r2); /* Recover some data */ const float mi = pi->mass; const float mj = pj->mass; const float rhoi = pi->rho; const float rhoj = pj->rho; const float rhoi_inv = 1.f / rhoi; const float rhoj_inv = 1.f / rhoj; const float pressurei = pi->force.pressure; const float pressurej = pj->force.pressure; /* Get the kernel for hi. */ const float hi_inv = 1.0f / hi; const float xi = r * hi_inv; float wi, wi_dx; kernel_deval(xi, &wi, &wi_dx); /* Get the kernel for hj. */ const float hj_inv = 1.0f / hj; const float xj = r * hj_inv; float wj, wj_dx; kernel_deval(xj, &wj, &wj_dx); /* Linear-order reproducing kernel gradient term (Sandnes+2025 Eqn. 28) */ float Gj[3], Gi[3], G_mean[3]; hydro_set_Gi_Gj_forceloop(Gi, Gj, pi, pj, dx, wi, wj, wi_dx, wj_dx); /* Antisymmetric kernel grad term for conservation of momentum and energy */ G_mean[0] = 0.5f * (Gi[0] - Gj[0]); G_mean[1] = 0.5f * (Gi[1] - Gj[1]); G_mean[2] = 0.5f * (Gi[2] - Gj[2]); /* Viscous pressures (Sandnes+2025 Eqn. 41) */ float Qi, Qj; float visc_signal_velocity, difn_signal_velocity; hydro_set_Qi_Qj(&Qi, &Qj, &visc_signal_velocity, &difn_signal_velocity, pi, pj, dx); /* Pressure terms to be used in evolution equations */ const float P_i_term = pressurei * rhoi_inv * rhoj_inv; const float P_j_term = pressurej * rhoi_inv * rhoj_inv; const float Q_i_term = Qi * rhoi_inv * rhoj_inv; const float Q_j_term = Qj * rhoi_inv * rhoj_inv; /* Use the force Luke! */ pi->a_hydro[0] -= mj * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[0]; pi->a_hydro[1] -= mj * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[1]; pi->a_hydro[2] -= mj * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[2]; pj->a_hydro[0] += mi * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[0]; pj->a_hydro[1] += mi * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[1]; pj->a_hydro[2] += mi * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[2]; /* v_ij dot kernel gradient term */ const float dvdotG = (pi->v[0] - pj->v[0]) * G_mean[0] + (pi->v[1] - pj->v[1]) * G_mean[1] + (pi->v[2] - pj->v[2]) * G_mean[2]; /* Internal energy time derivative */ pi->u_dt += mj * (P_i_term + Q_i_term) * dvdotG; pj->u_dt += mi * (P_j_term + Q_j_term) * dvdotG; /* Density time derivative */ pi->drho_dt += mj * (rhoi * rhoj_inv) * dvdotG; pj->drho_dt += mi * (rhoj * rhoi_inv) * dvdotG; /* Get the time derivative for h. */ pi->force.h_dt -= mj * dvdotG * rhoj_inv; pj->force.h_dt -= mi * dvdotG * rhoi_inv; const float v_sig = visc_signal_velocity; /* Update the signal velocity. */ pi->force.v_sig = max(pi->force.v_sig, v_sig); pj->force.v_sig = max(pj->force.v_sig, v_sig); if ((pi->is_h_max) || (pj->is_h_max)) { /* Do not add diffusion or normalising terms if either particle has h=h_max */ return; } /* Calculate some quantities */ const float mean_rho = 0.5f * (rhoi + rhoj); const float mean_rho_inv = 1.f / mean_rho; const float mean_balsara = 0.5f * (pi->force.balsara + pj->force.balsara); const float mod_G = sqrtf(G_mean[0] * G_mean[0] + G_mean[1] * G_mean[1] + G_mean[2] * G_mean[2]); const float v_sig_norm = sqrtf((pi->v[0] - pj->v[0]) * (pi->v[0] - pj->v[0]) + (pi->v[1] - pj->v[1]) * (pi->v[1] - pj->v[1]) + (pi->v[2] - pj->v[2]) * (pi->v[2] - pj->v[2])); /* Add normalising term to density evolution (Sandnes+2025 Eqn. 51) */ const float alpha_norm = const_remix_norm_alpha; float drho_dt_norm_and_difn_i = alpha_norm * mj * v_sig_norm * pi->force.vac_switch * (pi->m0 * rhoi - rhoi) * mod_G * mean_rho_inv; float drho_dt_norm_and_difn_j = alpha_norm * mi * v_sig_norm * pj->force.vac_switch * (pj->m0 * rhoj - rhoj) * mod_G * mean_rho_inv; /* Only include diffusion for same-material particle pair */ if (pi->mat_id == pj->mat_id) { /* Diffusion parameters */ const float a_difn_rho = const_remix_difn_a_rho; const float b_difn_rho = const_remix_difn_b_rho; const float a_difn_u = const_remix_difn_a_u; const float b_difn_u = const_remix_difn_b_u; float utilde_i, utilde_j, rhotilde_i, rhotilde_j; hydro_set_u_rho_difn(&utilde_i, &utilde_j, &rhotilde_i, &rhotilde_j, pi, pj, dx); const float v_sig_difn = difn_signal_velocity; /* Calculate artificial diffusion of internal energy (Sandnes+2025 Eqn. 42) */ const float du_dt_difn_i = -(a_difn_u + b_difn_u * mean_balsara) * mj * v_sig_difn * (utilde_i - utilde_j) * mod_G * mean_rho_inv; const float du_dt_difn_j = -(a_difn_u + b_difn_u * mean_balsara) * mi * v_sig_difn * (utilde_j - utilde_i) * mod_G * mean_rho_inv; /* Add artificial diffusion to evolution of internal energy */ pi->u_dt += du_dt_difn_i; pj->u_dt += du_dt_difn_j; /* Calculate artificial diffusion of density (Sandnes+2025 Eqn. 43) */ drho_dt_norm_and_difn_i += -(a_difn_rho + b_difn_rho * mean_balsara) * mj * (rhoi * rhoj_inv) * v_sig_difn * (rhotilde_i - rhotilde_j) * mod_G * mean_rho_inv; drho_dt_norm_and_difn_j += -(a_difn_rho + b_difn_rho * mean_balsara) * mi * (rhoj * rhoi_inv) * v_sig_difn * (rhotilde_j - rhotilde_i) * mod_G * mean_rho_inv; } /* Add normalising term and artificial diffusion to evolution of density */ pi->drho_dt += drho_dt_norm_and_difn_i; pj->drho_dt += drho_dt_norm_and_difn_j; } /** * @brief Force interaction between two particles (non-symmetric). * * @param r2 Comoving square distance between the two particles. * @param dx Comoving vector separating both particles (pi - pj). * @param hi Comoving smoothing-length of particle i. * @param hj Comoving smoothing-length of particle j. * @param pi First particle. * @param pj Second particle (not updated). * @param a Current scale factor. * @param H Current Hubble parameter. */ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force( const float r2, const float dx[3], const float hi, const float hj, struct part *restrict pi, const struct part *restrict pj, const float a, const float H) { #ifdef SWIFT_DEBUG_CHECKS if (pi->time_bin >= time_bin_inhibited) error("Inhibited pi in interaction function!"); if (pj->time_bin >= time_bin_inhibited) error("Inhibited pj in interaction function!"); #endif /* Get r. */ const float r = sqrtf(r2); /* Recover some data */ const float mj = pj->mass; const float rhoi = pi->rho; const float rhoj = pj->rho; const float rhoi_inv = 1.f / rhoi; const float rhoj_inv = 1.f / rhoj; const float pressurei = pi->force.pressure; const float pressurej = pj->force.pressure; /* Get the kernel for hi. */ const float hi_inv = 1.0f / hi; const float xi = r * hi_inv; float wi, wi_dx; kernel_deval(xi, &wi, &wi_dx); /* Get the kernel for hj. */ const float hj_inv = 1.0f / hj; const float xj = r * hj_inv; float wj, wj_dx; kernel_deval(xj, &wj, &wj_dx); /* Linear-order reproducing kernel gradient term (Sandnes+2025 Eqn. 28) */ float Gj[3], Gi[3], G_mean[3]; hydro_set_Gi_Gj_forceloop(Gi, Gj, pi, pj, dx, wi, wj, wi_dx, wj_dx); /* Antisymmetric kernel grad term for conservation of momentum and energy */ G_mean[0] = 0.5f * (Gi[0] - Gj[0]); G_mean[1] = 0.5f * (Gi[1] - Gj[1]); G_mean[2] = 0.5f * (Gi[2] - Gj[2]); /* Viscous pressures (Sandnes+2025 Eqn. 41) */ float Qi, Qj; float visc_signal_velocity, difn_signal_velocity; hydro_set_Qi_Qj(&Qi, &Qj, &visc_signal_velocity, &difn_signal_velocity, pi, pj, dx); /* Pressure terms to be used in evolution equations */ const float P_i_term = pressurei * rhoi_inv * rhoj_inv; const float P_j_term = pressurej * rhoi_inv * rhoj_inv; const float Q_i_term = Qi * rhoi_inv * rhoj_inv; const float Q_j_term = Qj * rhoi_inv * rhoj_inv; /* Use the force Luke! */ pi->a_hydro[0] -= mj * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[0]; pi->a_hydro[1] -= mj * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[1]; pi->a_hydro[2] -= mj * (P_i_term + P_j_term + Q_i_term + Q_j_term) * G_mean[2]; /* v_ij dot kernel gradient term */ const float dvdotG = (pi->v[0] - pj->v[0]) * G_mean[0] + (pi->v[1] - pj->v[1]) * G_mean[1] + (pi->v[2] - pj->v[2]) * G_mean[2]; /* Internal energy time derivative */ pi->u_dt += mj * (P_i_term + Q_i_term) * dvdotG; /* Density time derivative */ pi->drho_dt += mj * (rhoi * rhoj_inv) * dvdotG; /* Get the time derivative for h. */ pi->force.h_dt -= mj * dvdotG * rhoj_inv; const float v_sig = visc_signal_velocity; /* Update the signal velocity. */ pi->force.v_sig = max(pi->force.v_sig, v_sig); if ((pi->is_h_max) || (pj->is_h_max)) { /* Do not add diffusion or normalising terms if either particle has h=h_max */ return; } /* Calculate some quantities */ const float mean_rho = 0.5f * (rhoi + rhoj); const float mean_rho_inv = 1.f / mean_rho; const float mean_balsara = 0.5f * (pi->force.balsara + pj->force.balsara); const float mod_G = sqrtf(G_mean[0] * G_mean[0] + G_mean[1] * G_mean[1] + G_mean[2] * G_mean[2]); const float v_sig_norm = sqrtf((pi->v[0] - pj->v[0]) * (pi->v[0] - pj->v[0]) + (pi->v[1] - pj->v[1]) * (pi->v[1] - pj->v[1]) + (pi->v[2] - pj->v[2]) * (pi->v[2] - pj->v[2])); /* Add normalising term to density evolution (Sandnes+2025 Eqn. 51) */ const float alpha_norm = const_remix_norm_alpha; float drho_dt_norm_and_difn_i = alpha_norm * mj * v_sig_norm * pi->force.vac_switch * (pi->m0 * rhoi - rhoi) * mod_G * mean_rho_inv; /* Only include diffusion for same-material particle pair */ if (pi->mat_id == pj->mat_id) { /* Diffusion parameters */ const float a_difn_rho = const_remix_difn_a_rho; const float b_difn_rho = const_remix_difn_b_rho; const float a_difn_u = const_remix_difn_a_u; const float b_difn_u = const_remix_difn_b_u; float utilde_i, utilde_j, rhotilde_i, rhotilde_j; hydro_set_u_rho_difn(&utilde_i, &utilde_j, &rhotilde_i, &rhotilde_j, pi, pj, dx); const float v_sig_difn = difn_signal_velocity; /* Calculate artificial diffusion of internal energy (Sandnes+2025 Eqn. 42) */ const float du_dt_difn_i = -(a_difn_u + b_difn_u * mean_balsara) * mj * v_sig_difn * (utilde_i - utilde_j) * mod_G * mean_rho_inv; /* Add artificial diffusion to evolution of internal energy */ pi->u_dt += du_dt_difn_i; /* Calculate artificial diffusion of density (Sandnes+2025 Eqn. 43) */ drho_dt_norm_and_difn_i += -(a_difn_rho + b_difn_rho * mean_balsara) * mj * (rhoi * rhoj_inv) * v_sig_difn * (rhotilde_i - rhotilde_j) * mod_G * mean_rho_inv; } /* Add normalising term and artificial diffusion to evolution of density */ pi->drho_dt += drho_dt_norm_and_difn_i; } #endif /* SWIFT_REMIX_HYDRO_IACT_H */