Added files for minimal implementation of SPH

src/Makefile.am

@@ -47,6 +47,8 @@ AM_SOURCES = space.c runner.c queue.c task.c cell.c engine.c \
 noinst_HEADERS = approx_math.h atomic.h cycle.h error.h inline.h kernel.h vector.h \
 		 runner_doiact.h runner_doiact_grav.h units.h intrinsics.h \
 		 hydro.h hydro_io.h gravity.h \
+		 hydro/Minimal/hydro.h hydro/Minimal/hydro_iact.h hydro/Minimal/hydro_io.h \
+                 hydro/Minimal/hydro_debug.h hydro/Minimal/hydro_part.h
 		 hydro/Default/hydro.h hydro/Default/hydro_iact.h hydro/Default/hydro_io.h \
                  hydro/Default/hydro_debug.h hydro/Default/hydro_part.h \
 		 hydro/Gadget2/hydro.h hydro/Gadget2/hydro_iact.h hydro/Gadget2/hydro_io.h \

src/const.h

@@ -66,7 +66,9 @@
 #define const_iepsilon6 (const_iepsilon3* const_iepsilon3)
 
 /* SPH variant to use */
-#define GADGET2_SPH
+#define MINIMAL_SPH
+//#define GADGET2_SPH
+//#define DEFAULT_SPH
 
 /* System of units */
 #define const_unit_length_in_cgs 1   /* 3.08567810e16  /\* 1Mpc *\/ */

src/hydro/Minimal/hydro.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Coypright (c) 2015 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 <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+
+/**
+ * @brief Computes the hydro time-step of a given particle
+ *
+ * @param p Pointer to the particle data
+ * @param xp Pointer to the extended particle data
+ *
+ */
+__attribute__((always_inline)) INLINE static float hydro_compute_timestep(
+    struct part* p, struct xpart* xp) {
+
+  /* CFL condition */
+  float dt_cfl = 2.f * const_cfl * kernel_gamma * p->h / p->force.v_sig;
+
+  /* Limit change in u */
+  float dt_u_change = (p->force.u_dt != 0.0f)
+                          ? fabsf(const_max_u_change * p->u / p->force.u_dt)
+                          : FLT_MAX;
+
+  return fminf(dt_cfl, fminf(dt_h_change, dt_u_change));
+}
+
+/**
+ * @brief Prepares a particle for the density calculation.
+ *
+ * Zeroes all the relevant arrays in preparation for the sums taking place in
+ * the variaous density tasks
+ *
+ * @param p The particle to act upon
+ */
+__attribute__((always_inline))
+    INLINE static void hydro_init_part(struct part* p) {
+  p->density.wcount = 0.f;
+  p->density.wcount_dh = 0.f;
+  p->rho = 0.f;
+  p->rho_dh = 0.f;
+  p->density.div_v = 0.f;
+  p->density.curl_v[0] = 0.f;
+  p->density.curl_v[1] = 0.f;
+  p->density.curl_v[2] = 0.f;
+}
+
+/**
+ * @brief Finishes the density calculation.
+ *
+ * Multiplies the density and number of neighbours by the appropiate constants
+ * and add the self-contribution term.
+ *
+ * @param p The particle to act upon
+ * @param time The current time
+ */
+__attribute__((always_inline))
+    INLINE static void hydro_end_density(struct part* p, float time) {
+
+  /* Some smoothing length multiples. */
+  const float h = p->h;
+  const float ih = 1.0f / h;
+  const float ih2 = ih * ih;
+  const float ih4 = ih2 * ih2;
+
+  /* Final operation on the density. */
+  p->rho = ih * ih2 * (p->rho + p->mass * kernel_root);
+  p->rho_dh = (p->rho_dh - 3.0f * p->mass * kernel_root) * ih4;
+  p->density.wcount =
+      (p->density.wcount + kernel_root) * (4.0f / 3.0 * M_PI * kernel_gamma3);
+  p->density.wcount_dh =
+      p->density.wcount_dh * ih * (4.0f / 3.0 * M_PI * kernel_gamma3);
+}
+
+/**
+ * @brief Prepare a particle for the force calculation.
+ *
+ * Computes viscosity term, conduction term and smoothing length gradient terms.
+ *
+ * @param p The particle to act upon
+ * @param xp The extended particle data to act upon
+ * @param time The current time
+ */
+__attribute__((always_inline))
+INLINE static void hydro_prepare_force(struct part* p, struct xpart* xp, float time) {
+
+  /* Some smoothing length multiples. */
+  const float h = p->h;
+  const float ih = 1.0f / h;
+  const float ih2 = ih * ih;
+  const float ih4 = ih2 * ih2;
+
+  /* Pre-compute some stuff for the balsara switch. */
+  const float normDiv_v = fabs(p->density.div_v / p->rho * ih4);
+  const float normCurl_v = sqrtf(p->density.curl_v[0] * p->density.curl_v[0] +
+                                 p->density.curl_v[1] * p->density.curl_v[1] +
+                                 p->density.curl_v[2] * p->density.curl_v[2]) /
+                           p->rho * ih4;
+
+  /* Compute this particle's sound speed. */
+  const float u = p->u;
+  const float fc = p->force.c =
+      sqrtf(const_hydro_gamma * (const_hydro_gamma - 1.0f) * u);
+
+  /* Compute the P/Omega/rho2. */
+  xp->omega = 1.0f + 0.3333333333f * h * p->rho_dh / p->rho;
+  p->force.POrho2 = u * (const_hydro_gamma - 1.0f) / (p->rho * xp->omega);
+
+  /* Balsara switch */
+  p->force.balsara = normDiv_v / (normDiv_v + normCurl_v + 0.0001f * fc * ih);
+
+  /* Viscosity parameter decay time */
+  const float tau = h / (2.f * const_viscosity_length * p->force.c);
+
+  /* Viscosity source term */
+  const float S = fmaxf(-normDiv_v, 0.f);
+
+  /* Compute the particle's viscosity parameter time derivative */
+  const float alpha_dot = (const_viscosity_alpha_min - p->alpha) / tau +
+                          (const_viscosity_alpha_max - p->alpha) * S;
+
+  /* Update particle's viscosity paramter */
+  p->alpha += alpha_dot * (p->t_end - p->t_begin);
+}
+
+/**
+ * @brief Reset acceleration fields of a particle
+ *
+ * Resets all hydro acceleration and time derivative fields in preparation
+ * for the sums taking place in the variaous force tasks
+ *
+ * @param p The particle to act upon
+ */
+__attribute__((always_inline))
+    INLINE static void hydro_reset_acceleration(struct part* p) {
+
+  /* Reset the acceleration. */
+  p->a_hydro[0] = 0.0f;
+  p->a_hydro[1] = 0.0f;
+  p->a_hydro[2] = 0.0f;
+
+  /* Reset the time derivatives. */
+  p->force.u_dt = 0.0f;
+  p->h_dt = 0.0f;
+  p->force.v_sig = 0.0f;
+}
+
+/**
+ * @brief Predict additional particle fields forward in time when drifting
+ *
+ * @param p The particle
+ * @param xp The extended data of the particle
+ * @param t0 The time at the start of the drift
+ * @param t1 The time at the end of the drift
+ */
+__attribute__((always_inline)) INLINE static void hydro_predict_extra(
+    struct part* p, struct xpart* xp, float t0, float t1) {
+  float u, w;
+
+  const float dt = t1 - t0;
+
+  /* Predict internal energy */
+  w = p->force.u_dt / p->u * dt;
+  if (fabsf(w) < 0.01f) /* 1st order expansion of exp(w) */
+    u = p->u *=
+        1.0f + w * (1.0f + w * (0.5f + w * (1.0f / 6.0f + 1.0f / 24.0f * w)));
+  else
+    u = p->u *= expf(w);
+
+  /* Predict gradient term */
+  p->force.POrho2 = u * (const_hydro_gamma - 1.0f) / (p->rho * xp->omega);
+}
+
+/**
+ * @brief Finishes the force calculation.
+ *
+ * Multiplies the forces and accelerationsby the appropiate constants
+ *
+ * @param p The particle to act upon
+ */
+__attribute__((always_inline))
+    INLINE static void hydro_end_force(struct part* p) {}
+
+/**
+ * @brief Kick the additional variables
+ *
+ * @param p The particle to act upon
+ * @param dt The time-step for this kick
+ */
+__attribute__((always_inline))
+    INLINE static void hydro_kick_extra(struct part* p, float dt) {}
+
+/**
+ * @brief Converts hydro quantity of a particle
+ *
+ * Requires the density to be known
+ *
+ * @param p The particle to act upon
+ */
+__attribute__((always_inline))
+    INLINE static void hydro_convert_quantities(struct part* p) {}

src/hydro/Minimal/hydro_debug.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Coypright (c) 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 <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+
+__attribute__((always_inline))
+    INLINE static void hydro_debug_particle(struct part* p, struct xpart* xp) {
+  printf(
+      "x=[%.3e,%.3e,%.3e], "
+      "v=[%.3e,%.3e,%.3e],v_full=[%.3e,%.3e,%.3e] \n a=[%.3e,%.3e,%.3e],\n "
+      "h=%.3e, "
+      "wcount=%d, m=%.3e, dh_drho=%.3e, rho=%.3e, t_begin=%.3e, t_end=%.3e\n",
+      p->x[0], p->x[1], p->x[2], p->v[0], p->v[1], p->v[2], xp->v_full[0],
+      xp->v_full[1], xp->v_full[2], p->a_hydro[0], p->a_hydro[1], p->a_hydro[2],
+      p->h, (int)p->density.wcount, p->mass, p->rho_dh, p->rho, p->t_begin,
+      p->t_end);
+}

src/hydro/Minimal/hydro_iact.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2012 Pedro Gonnet (pedro.gonnet@durham.ac.uk)
+ *                    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 <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_RUNNER_IACT_H
+#define SWIFT_RUNNER_IACT_H
+
+/* Includes. */
+#include "const.h"
+#include "kernel.h"
+#include "part.h"
+#include "vector.h"
+
+/**
+ * @brief SPH interaction functions following the Gadget-2 version of SPH.
+ *
+ * The interactions computed here are the ones presented in the Gadget-2 paper
+ *and use the same
+ * numerical coefficients as the Gadget-2 code. When used with the Spline-3
+ *kernel, the results
+ * should be equivalent to the ones obtained with Gadget-2 up to the rounding
+ *errors and interactions
+ * missed by the Gadget-2 tree-code neighbours search.
+ *
+ * The code uses internal energy instead of entropy as a thermodynamical
+ *variable.
+ */
+
+/**
+ * @brief Density loop
+ */
+
+__attribute__((always_inline)) INLINE static void runner_iact_density(
+    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+
+  float r = sqrtf(r2), ri = 1.0f / r;
+  float xi, xj;
+  float h_inv;
+  float wi, wj, wi_dx, wj_dx;
+  float mi, mj;
+  float dvdr;
+  float dv[3], curlvr[3];
+  int k;
+
+  /* Get the masses. */
+  mi = pi->mass;
+  mj = pj->mass;
+
+  /* Compute dv dot r */
+  dv[0] = pi->v[0] - pj->v[0];
+  dv[1] = pi->v[1] - pj->v[1];
+  dv[2] = pi->v[2] - pj->v[2];
+  dvdr = dv[0] * dx[0] + dv[1] * dx[1] + dv[2] * dx[2];
+  dvdr *= ri;
+
+  /* Compute dv cross r */
+  curlvr[0] = dv[1] * dx[2] - dv[2] * dx[1];
+  curlvr[1] = dv[2] * dx[0] - dv[0] * dx[2];
+  curlvr[2] = dv[0] * dx[1] - dv[1] * dx[0];
+  for (k = 0; k < 3; k++) curlvr[k] *= ri;
+
+  /* Compute density of pi. */
+  h_inv = 1.0 / hi;
+  xi = r * h_inv;
+  kernel_deval(xi, &wi, &wi_dx);
+
+  pi->rho += mj * wi;
+  pi->rho_dh -= mj * (3.0 * wi + xi * wi_dx);
+  pi->density.wcount += wi;
+  pi->density.wcount_dh -= xi * wi_dx;
+
+  pi->density.div_v += mj * dvdr * wi_dx;
+  for (k = 0; k < 3; k++) pi->density.curl_v[k] += mj * curlvr[k] * wi_dx;
+
+  /* Compute density of pj. */
+  h_inv = 1.0 / hj;
+  xj = r * h_inv;
+  kernel_deval(xj, &wj, &wj_dx);
+
+  pj->rho += mi * wj;
+  pj->rho_dh -= mi * (3.0 * wj + xj * wj_dx);
+  pj->density.wcount += wj;
+  pj->density.wcount_dh -= xj * wj_dx;
+
+  pj->density.div_v += mi * dvdr * wj_dx;
+  for (k = 0; k < 3; k++) pj->density.curl_v[k] += mi * curlvr[k] * wj_dx;
+}
+
+/**
+ * @brief Density loop (Vectorized version)
+ */
+__attribute__((always_inline)) INLINE static void runner_iact_vec_density(
+    float *R2, float *Dx, float *Hi, float *Hj, struct part **pi,
+    struct part **pj) {
+
+#ifdef VECTORIZE
+
+  vector r, ri, r2, xi, xj, hi, hj, hi_inv, hj_inv, wi, wj, wi_dx, wj_dx;
+  vector rhoi, rhoj, rhoi_dh, rhoj_dh, wcounti, wcountj, wcounti_dh, wcountj_dh;
+  vector mi, mj;
+  vector dx[3], dv[3];
+  vector vi[3], vj[3];
+  vector dvdr, div_vi, div_vj;
+  vector curlvr[3], curl_vi[3], curl_vj[3];
+  int k, j;
+
+#if VEC_SIZE == 8
+  mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass,
+                 pi[4]->mass, pi[5]->mass, pi[6]->mass, pi[7]->mass);
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
+                 pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k],
+                      pi[4]->v[k], pi[5]->v[k], pi[6]->v[k], pi[7]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k],
+                      pj[4]->v[k], pj[5]->v[k], pj[6]->v[k], pj[7]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k], Dx[12 + k],
+                      Dx[15 + k], Dx[18 + k], Dx[21 + k]);
+#elif VEC_SIZE == 4
+  mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass);
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k]);
+#endif
+
+  /* Get the radius and inverse radius. */
+  r2.v = vec_load(R2);
+  ri.v = vec_rsqrt(r2.v);
+  ri.v = ri.v - vec_set1(0.5f) * ri.v * (r2.v * ri.v * ri.v - vec_set1(1.0f));
+  r.v = r2.v * ri.v;
+
+  hi.v = vec_load(Hi);
+  hi_inv.v = vec_rcp(hi.v);
+  hi_inv.v = hi_inv.v - hi_inv.v * (hi_inv.v * hi.v - vec_set1(1.0f));
+  xi.v = r.v * hi_inv.v;
+
+  hj.v = vec_load(Hj);
+  hj_inv.v = vec_rcp(hj.v);
+  hj_inv.v = hj_inv.v - hj_inv.v * (hj_inv.v * hj.v - vec_set1(1.0f));
+  xj.v = r.v * hj_inv.v;
+
+  kernel_deval_vec(&xi, &wi, &wi_dx);
+  kernel_deval_vec(&xj, &wj, &wj_dx);
+
+  /* Compute dv. */
+  dv[0].v = vi[0].v - vj[0].v;
+  dv[1].v = vi[1].v - vj[1].v;
+  dv[2].v = vi[2].v - vj[2].v;
+
+  /* Compute dv dot r */
+  dvdr.v = (dv[0].v * dx[0].v) + (dv[1].v * dx[1].v) + (dv[2].v * dx[2].v);
+  dvdr.v = dvdr.v * ri.v;
+
+  /* Compute dv cross r */
+  curlvr[0].v = dv[1].v * dx[2].v - dv[2].v * dx[1].v;
+  curlvr[1].v = dv[2].v * dx[0].v - dv[0].v * dx[2].v;
+  curlvr[2].v = dv[0].v * dx[1].v - dv[1].v * dx[0].v;
+  for (k = 0; k < 3; k++) curlvr[k].v *= ri.v;
+
+  rhoi.v = mj.v * wi.v;
+  rhoi_dh.v = mj.v * (vec_set1(3.0f) * wi.v + xi.v * wi_dx.v);
+  wcounti.v = wi.v;
+  wcounti_dh.v = xi.v * wi_dx.v;
+  div_vi.v = mj.v * dvdr.v * wi_dx.v;
+  for (k = 0; k < 3; k++) curl_vi[k].v = mj.v * curlvr[k].v * wi_dx.v;
+
+  rhoj.v = mi.v * wj.v;
+  rhoj_dh.v = mi.v * (vec_set1(3.0f) * wj.v + xj.v * wj_dx.v);
+  wcountj.v = wj.v;
+  wcountj_dh.v = xj.v * wj_dx.v;
+  div_vj.v = mi.v * dvdr.v * wj_dx.v;
+  for (k = 0; k < 3; k++) curl_vj[k].v = mi.v * curlvr[k].v * wj_dx.v;
+
+  for (k = 0; k < VEC_SIZE; k++) {
+    pi[k]->rho += rhoi.f[k];
+    pi[k]->rho_dh -= rhoi_dh.f[k];
+    pi[k]->density.wcount += wcounti.f[k];
+    pi[k]->density.wcount_dh -= wcounti_dh.f[k];
+    pi[k]->density.div_v += div_vi.f[k];
+    for (j = 0; j < 3; j++) pi[k]->density.curl_v[j] += curl_vi[j].f[k];
+    pj[k]->rho += rhoj.f[k];
+    pj[k]->rho_dh -= rhoj_dh.f[k];
+    pj[k]->density.wcount += wcountj.f[k];
+    pj[k]->density.wcount_dh -= wcountj_dh.f[k];
+    pj[k]->density.div_v += div_vj.f[k];
+    for (j = 0; j < 3; j++) pj[k]->density.curl_v[j] += curl_vj[j].f[k];
+  }
+
+#else
+
+  for (int k = 0; k < VEC_SIZE; k++)
+    runner_iact_density(R2[k], &Dx[3 * k], Hi[k], Hj[k], pi[k], pj[k]);
+
+#endif
+}
+
+/**
+ * @brief Density loop (non-symmetric version)
+ */
+
+__attribute__((always_inline)) INLINE static void runner_iact_nonsym_density(
+    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+
+  float r, ri;
+  float xi;
+  float h_inv;
+  float wi, wi_dx;
+  float mj;
+  float dvdr;
+  float dv[3], curlvr[3];
+  int k;
+
+  /* Get the masses. */
+  mj = pj->mass;
+
+  /* Get r and r inverse. */
+  r = sqrtf(r2);
+  ri = 1.0f / r;
+
+  /* Compute dv dot r */
+  dv[0] = pi->v[0] - pj->v[0];
+  dv[1] = pi->v[1] - pj->v[1];
+  dv[2] = pi->v[2] - pj->v[2];
+  dvdr = dv[0] * dx[0] + dv[1] * dx[1] + dv[2] * dx[2];
+  dvdr *= ri;
+
+  /* Compute dv cross r */
+  curlvr[0] = dv[1] * dx[2] - dv[2] * dx[1];
+  curlvr[1] = dv[2] * dx[0] - dv[0] * dx[2];
+  curlvr[2] = dv[0] * dx[1] - dv[1] * dx[0];
+  for (k = 0; k < 3; k++) curlvr[k] *= ri;
+
+  h_inv = 1.0 / hi;
+  xi = r * h_inv;
+  kernel_deval(xi, &wi, &wi_dx);
+
+  pi->rho += mj * wi;
+  pi->rho_dh -= mj * (3.0 * wi + xi * wi_dx);
+  pi->density.wcount += wi;
+  pi->density.wcount_dh -= xi * wi_dx;
+
+  pi->density.div_v += mj * dvdr * wi_dx;
+  for (k = 0; k < 3; k++) pi->density.curl_v[k] += mj * curlvr[k] * wi_dx;
+}
+
+/**
+ * @brief Density loop (non-symmetric vectorized version)
+ */
+
+__attribute__((always_inline))
+    INLINE static void runner_iact_nonsym_vec_density(float *R2, float *Dx,
+                                                      float *Hi, float *Hj,
+                                                      struct part **pi,
+                                                      struct part **pj) {
+
+#ifdef VECTORIZE
+
+  vector r, ri, r2, xi, hi, hi_inv, wi, wi_dx;
+  vector rhoi, rhoi_dh, wcounti, wcounti_dh, div_vi;
+  vector mj;
+  vector dx[3], dv[3];
+  vector vi[3], vj[3];
+  vector dvdr;
+  vector curlvr[3], curl_vi[3];
+  int k, j;
+
+#if VEC_SIZE == 8
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
+                 pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k],
+                      pi[4]->v[k], pi[5]->v[k], pi[6]->v[k], pi[7]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k],
+                      pj[4]->v[k], pj[5]->v[k], pj[6]->v[k], pj[7]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k], Dx[12 + k],
+                      Dx[15 + k], Dx[18 + k], Dx[21 + k]);
+#elif VEC_SIZE == 4
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k]);
+#endif
+
+  /* Get the radius and inverse radius. */
+  r2.v = vec_load(R2);
+  ri.v = vec_rsqrt(r2.v);
+  ri.v = ri.v - vec_set1(0.5f) * ri.v * (r2.v * ri.v * ri.v - vec_set1(1.0f));
+  r.v = r2.v * ri.v;
+
+  hi.v = vec_load(Hi);
+  hi_inv.v = vec_rcp(hi.v);
+  hi_inv.v = hi_inv.v - hi_inv.v * (hi_inv.v * hi.v - vec_set1(1.0f));
+  xi.v = r.v * hi_inv.v;
+
+  kernel_deval_vec(&xi, &wi, &wi_dx);
+
+  /* Compute dv. */
+  dv[0].v = vi[0].v - vj[0].v;
+  dv[1].v = vi[1].v - vj[1].v;
+  dv[2].v = vi[2].v - vj[2].v;
+
+  /* Compute dv dot r */
+  dvdr.v = (dv[0].v * dx[0].v) + (dv[1].v * dx[1].v) + (dv[2].v * dx[2].v);
+  dvdr.v = dvdr.v * ri.v;
+
+  /* Compute dv cross r */
+  curlvr[0].v = dv[1].v * dx[2].v - dv[2].v * dx[1].v;
+  curlvr[1].v = dv[2].v * dx[0].v - dv[0].v * dx[2].v;
+  curlvr[2].v = dv[0].v * dx[1].v - dv[1].v * dx[0].v;
+  for (k = 0; k < 3; k++) curlvr[k].v *= ri.v;
+
+  rhoi.v = mj.v * wi.v;
+  rhoi_dh.v = mj.v * (vec_set1(3.0f) * wi.v + xi.v * wi_dx.v);
+  wcounti.v = wi.v;
+  wcounti_dh.v = xi.v * wi_dx.v;
+  div_vi.v = mj.v * dvdr.v * wi_dx.v;
+  for (k = 0; k < 3; k++) curl_vi[k].v = mj.v * curlvr[k].v * wi_dx.v;
+
+  for (k = 0; k < VEC_SIZE; k++) {
+    pi[k]->rho += rhoi.f[k];
+    pi[k]->rho_dh -= rhoi_dh.f[k];
+    pi[k]->density.wcount += wcounti.f[k];
+    pi[k]->density.wcount_dh -= wcounti_dh.f[k];
+    pi[k]->density.div_v += div_vi.f[k];
+    for (j = 0; j < 3; j++) pi[k]->density.curl_v[j] += curl_vi[j].f[k];
+  }
+
+#else
+
+  for (int k = 0; k < VEC_SIZE; k++)
+    runner_iact_nonsym_density(R2[k], &Dx[3 * k], Hi[k], Hj[k], pi[k], pj[k]);
+
+#endif
+}
+
+/**
+ * @brief Force loop
+ */
+
+__attribute__((always_inline)) INLINE static void runner_iact_force(
+    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+
+  float r = sqrtf(r2), ri = 1.0f / r;
+  float xi, xj;
+  float hi_inv, hi2_inv;
+  float hj_inv, hj2_inv;
+  float wi, wj, wi_dx, wj_dx, wi_dr, wj_dr, w, dvdr;
+  float mi, mj, POrho2i, POrho2j, rhoi, rhoj;
+  float v_sig, omega_ij, Pi_ij, alpha_ij, tc, v_sig_u;
+  float f;
+  int k;
+
+  /* Get some values in local variables. */
+  mi = pi->mass;
+  mj = pj->mass;
+  rhoi = pi->rho;
+  rhoj = pj->rho;
+  POrho2i = pi->force.POrho2;
+  POrho2j = pj->force.POrho2;
+
+  /* Get the kernel for hi. */
+  hi_inv = 1.0f / hi;
+  hi2_inv = hi_inv * hi_inv;
+  xi = r * hi_inv;
+  kernel_deval(xi, &wi, &wi_dx);
+  wi_dr = hi2_inv * hi2_inv * wi_dx;
+
+  /* Get the kernel for hj. */
+  hj_inv = 1.0f / hj;
+  hj2_inv = hj_inv * hj_inv;
+  xj = r * hj_inv;
+  kernel_deval(xj, &wj, &wj_dx);
+  wj_dr = hj2_inv * hj2_inv * wj_dx;
+
+  /* Compute dv dot r. */
+  dvdr = (pi->v[0] - pj->v[0]) * dx[0] + (pi->v[1] - pj->v[1]) * dx[1] +
+         (pi->v[2] - pj->v[2]) * dx[2];
+  dvdr *= ri;
+
+  /* Compute the relative velocity. (This is 0 if the particles move away from
+   * each other and negative otherwise) */
+  omega_ij = fminf(dvdr, 0.f);
+
+  /* Compute signal velocity */
+  v_sig = pi->force.c + pj->force.c - 2.0f * omega_ij;
+
+  /* Compute viscosity parameter */
+  alpha_ij = -0.5f * (pi->alpha + pj->alpha);
+
+  /* Compute viscosity tensor */
+  Pi_ij = alpha_ij * v_sig * omega_ij / (rhoi + rhoj);
+
+  /* Apply balsara switch */
+  Pi_ij *= (pi->force.balsara + pj->force.balsara);
+
+  /* Thermal conductivity */
+  v_sig_u = sqrtf(2.f * (const_hydro_gamma - 1.f) *
+                  fabs(rhoi * pi->u - rhoj * pj->u) / (rhoi + rhoj));
+  tc = const_conductivity_alpha * v_sig_u / (rhoi + rhoj);
+  tc *= (wi_dr + wj_dr);
+
+  /* Get the common factor out. */
+  w = ri *
+      ((POrho2i * wi_dr + POrho2j * wj_dr) + 0.25f * Pi_ij * (wi_dr + wj_dr));
+
+  /* Use the force, Luke! */
+  for (k = 0; k < 3; k++) {
+    f = dx[k] * w;
+    pi->a_hydro[k] -= mj * f;
+    pj->a_hydro[k] += mi * f;
+  }
+
+  /* Get the time derivative for u. */
+  pi->force.u_dt +=
+      mj * dvdr * (POrho2i * wi_dr + 0.125f * Pi_ij * (wi_dr + wj_dr));
+  pj->force.u_dt +=
+      mi * dvdr * (POrho2j * wj_dr + 0.125f * Pi_ij * (wi_dr + wj_dr));
+
+  /* Add the thermal conductivity */
+  pi->force.u_dt += mj * tc * (pi->u - pj->u);
+  pj->force.u_dt += mi * tc * (pj->u - pi->u);
+
+  /* Get the time derivative for h. */
+  pi->h_dt -= mj * dvdr / rhoj * wi_dr;
+  pj->h_dt -= mi * dvdr / rhoi * wj_dr;
+
+  /* Update the signal velocity. */
+  pi->force.v_sig = fmaxf(pi->force.v_sig, v_sig);
+  pj->force.v_sig = fmaxf(pj->force.v_sig, v_sig);
+}
+
+/**
+ * @brief Force loop (Vectorized version)
+ */
+
+__attribute__((always_inline)) INLINE static void runner_iact_vec_force(
+    float *R2, float *Dx, float *Hi, float *Hj, struct part **pi,
+    struct part **pj) {
+
+#ifdef VECTORIZE
+
+  vector r, r2, ri;
+  vector xi, xj;
+  vector hi, hj, hi_inv, hj_inv;
+  vector hi2_inv, hj2_inv;
+  vector wi, wj, wi_dx, wj_dx, wi_dr, wj_dr, dvdr;
+  vector w;
+  vector piPOrho2, pjPOrho2, pirho, pjrho, piu, pju;
+  vector mi, mj;
+  vector f;
+  vector dx[3];
+  vector vi[3], vj[3];
+  vector pia[3], pja[3];
+  vector piu_dt, pju_dt;
+  vector pih_dt, pjh_dt;
+  vector ci, cj, v_sig, vi_sig, vj_sig;
+  vector omega_ij, Pi_ij, balsara;
+  vector pialpha, pjalpha, alpha_ij, v_sig_u, tc;
+  int j, k;
+
+/* Load stuff. */
+#if VEC_SIZE == 8
+  mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass,
+                 pi[4]->mass, pi[5]->mass, pi[6]->mass, pi[7]->mass);
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
+                 pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
+  piPOrho2.v =
+      vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2, pi[2]->force.POrho2,
+              pi[3]->force.POrho2, pi[4]->force.POrho2, pi[5]->force.POrho2,
+              pi[6]->force.POrho2, pi[7]->force.POrho2);
+  pjPOrho2.v =
+      vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2, pj[2]->force.POrho2,
+              pj[3]->force.POrho2, pj[4]->force.POrho2, pj[5]->force.POrho2,
+              pj[6]->force.POrho2, pj[7]->force.POrho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho, pi[4]->rho,
+                    pi[5]->rho, pi[6]->rho, pi[7]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho, pj[4]->rho,
+                    pj[5]->rho, pj[6]->rho, pj[7]->rho);
+  piu.v = vec_set(pi[0]->u, pi[1]->u, pi[2]->u, pi[3]->u, pi[4]->u, pi[5]->u,
+                  pi[6]->u, pi[7]->u);
+  pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u, pj[4]->u, pj[5]->u,
+                  pj[6]->u, pj[7]->u);
+  ci.v =
+      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c,
+              pi[4]->force.c, pi[5]->force.c, pi[6]->force.c, pi[7]->force.c);
+  cj.v =
+      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c,
+              pj[4]->force.c, pj[5]->force.c, pj[6]->force.c, pj[7]->force.c);
+  vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
+                     pi[3]->force.v_sig, pi[4]->force.v_sig, pi[5]->force.v_sig,
+                     pi[6]->force.v_sig, pi[7]->force.v_sig);
+  vj_sig.v = vec_set(pj[0]->force.v_sig, pj[1]->force.v_sig, pj[2]->force.v_sig,
+                     pj[3]->force.v_sig, pj[4]->force.v_sig, pj[5]->force.v_sig,
+                     pj[6]->force.v_sig, pj[7]->force.v_sig);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k],
+                      pi[4]->v[k], pi[5]->v[k], pi[6]->v[k], pi[7]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k],
+                      pj[4]->v[k], pj[5]->v[k], pj[6]->v[k], pj[7]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k], Dx[12 + k],
+                      Dx[15 + k], Dx[18 + k], Dx[21 + k]);
+  balsara.v =
+      vec_set(pi[0]->force.balsara, pi[1]->force.balsara, pi[2]->force.balsara,
+              pi[3]->force.balsara, pi[4]->force.balsara, pi[5]->force.balsara,
+              pi[6]->force.balsara, pi[7]->force.balsara) +
+      vec_set(pj[0]->force.balsara, pj[1]->force.balsara, pj[2]->force.balsara,
+              pj[3]->force.balsara, pj[4]->force.balsara, pj[5]->force.balsara,
+              pj[6]->force.balsara, pj[7]->force.balsara);
+  pialpha.v = vec_set(pi[0]->alpha, pi[1]->alpha, pi[2]->alpha, pi[3]->alpha,
+                      pi[4]->alpha, pi[5]->alpha, pi[6]->alpha, pi[7]->alpha);
+  pjalpha.v = vec_set(pj[0]->alpha, pj[1]->alpha, pj[2]->alpha, pj[3]->alpha,
+                      pj[4]->alpha, pj[5]->alpha, pj[6]->alpha, pj[7]->alpha);
+#elif VEC_SIZE == 4
+  mi.v = vec_set(pi[0]->mass, pi[1]->mass, pi[2]->mass, pi[3]->mass);
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
+  piPOrho2.v = vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2,
+                       pi[2]->force.POrho2, pi[3]->force.POrho2);
+  pjPOrho2.v = vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2,
+                       pj[2]->force.POrho2, pj[3]->force.POrho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho);
+  piu.v = vec_set(pi[0]->u, pi[1]->u, pi[2]->u, pi[3]->u);
+  pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u);
+  ci.v =
+      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c);
+  cj.v =
+      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c);
+  vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
+                     pi[3]->force.v_sig);
+  vj_sig.v = vec_set(pj[0]->force.v_sig, pj[1]->force.v_sig, pj[2]->force.v_sig,
+                     pj[3]->force.v_sig);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k]);
+  balsara.v = vec_set(pi[0]->force.balsara, pi[1]->force.balsara,
+                      pi[2]->force.balsara, pi[3]->force.balsara) +
+              vec_set(pj[0]->force.balsara, pj[1]->force.balsara,
+                      pj[2]->force.balsara, pj[3]->force.balsara);
+  pialpha.v = vec_set(pi[0]->alpha, pi[1]->alpha, pi[2]->alpha, pi[3]->alpha);
+  pjalpha.v = vec_set(pj[0]->alpha, pj[1]->alpha, pj[2]->alpha, pj[3]->alpha);
+#else
+#error
+#endif
+
+  /* Get the radius and inverse radius. */
+  r2.v = vec_load(R2);
+  ri.v = vec_rsqrt(r2.v);
+  ri.v = ri.v - vec_set1(0.5f) * ri.v * (r2.v * ri.v * ri.v - vec_set1(1.0f));
+  r.v = r2.v * ri.v;
+
+  /* Get the kernel for hi. */
+  hi.v = vec_load(Hi);
+  hi_inv.v = vec_rcp(hi.v);
+  hi_inv.v = hi_inv.v - hi_inv.v * (hi.v * hi_inv.v - vec_set1(1.0f));
+  hi2_inv.v = hi_inv.v * hi_inv.v;
+  xi.v = r.v * hi_inv.v;
+  kernel_deval_vec(&xi, &wi, &wi_dx);
+  wi_dr.v = hi2_inv.v * hi2_inv.v * wi_dx.v;
+
+  /* Get the kernel for hj. */
+  hj.v = vec_load(Hj);
+  hj_inv.v = vec_rcp(hj.v);
+  hj_inv.v = hj_inv.v - hj_inv.v * (hj.v * hj_inv.v - vec_set1(1.0f));
+  hj2_inv.v = hj_inv.v * hj_inv.v;
+  xj.v = r.v * hj_inv.v;
+  kernel_deval_vec(&xj, &wj, &wj_dx);
+  wj_dr.v = hj2_inv.v * hj2_inv.v * wj_dx.v;
+
+  /* Compute dv dot r. */
+  dvdr.v = ((vi[0].v - vj[0].v) * dx[0].v) + ((vi[1].v - vj[1].v) * dx[1].v) +
+           ((vi[2].v - vj[2].v) * dx[2].v);
+  dvdr.v = dvdr.v * ri.v;
+
+  /* Get the time derivative for h. */
+  pih_dt.v = mj.v / pjrho.v * dvdr.v * wi_dr.v;
+  pjh_dt.v = mi.v / pirho.v * dvdr.v * wj_dr.v;
+
+  /* Compute the relative velocity. (This is 0 if the particles move away from
+   * each other and negative otherwise) */
+  omega_ij.v = vec_fmin(dvdr.v, vec_set1(0.0f));
+
+  /* Compute signal velocity */
+  v_sig.v = ci.v + cj.v - vec_set1(2.0f) * omega_ij.v;
+
+  /* Compute viscosity parameter */
+  alpha_ij.v = vec_set1(-0.5f) * (pialpha.v + pjalpha.v);
+
+  /* Compute viscosity tensor */
+  Pi_ij.v = balsara.v * alpha_ij.v * v_sig.v * omega_ij.v / (pirho.v + pjrho.v);
+  Pi_ij.v *= (wi_dr.v + wj_dr.v);
+
+  /* Thermal conductivity */
+  v_sig_u.v = vec_sqrt(vec_set1(2.f * (const_hydro_gamma - 1.f)) *
+                       vec_fabs(pirho.v * piu.v - pjrho.v * pju.v) /
+                       (pirho.v + pjrho.v));
+  tc.v = vec_set1(const_conductivity_alpha) * v_sig_u.v / (pirho.v + pjrho.v);
+  tc.v *= (wi_dr.v + wj_dr.v);
+
+  /* Get the common factor out. */
+  w.v = ri.v * ((piPOrho2.v * wi_dr.v + pjPOrho2.v * wj_dr.v) +
+                vec_set1(0.25f) * Pi_ij.v);
+
+  /* Use the force, Luke! */
+  for (k = 0; k < 3; k++) {
+    f.v = dx[k].v * w.v;
+    pia[k].v = mj.v * f.v;
+    pja[k].v = mi.v * f.v;
+  }
+
+  /* Get the time derivative for u. */
+  piu_dt.v =
+      mj.v * dvdr.v * (piPOrho2.v * wi_dr.v + vec_set1(0.125f) * Pi_ij.v);
+  pju_dt.v =
+      mi.v * dvdr.v * (pjPOrho2.v * wj_dr.v + vec_set1(0.125f) * Pi_ij.v);
+
+  /* Add the thermal conductivity */
+  piu_dt.v += mj.v * tc.v * (piu.v - pju.v);
+  pju_dt.v += mi.v * tc.v * (pju.v - piu.v);
+
+  /* compute the signal velocity (this is always symmetrical). */
+  vi_sig.v = vec_fmax(vi_sig.v, v_sig.v);
+  vj_sig.v = vec_fmax(vj_sig.v, v_sig.v);
+
+  /* Store the forces back on the particles. */
+  for (k = 0; k < VEC_SIZE; k++) {
+    pi[k]->force.u_dt += piu_dt.f[k];
+    pj[k]->force.u_dt += pju_dt.f[k];
+    pi[k]->h_dt -= pih_dt.f[k];
+    pj[k]->h_dt -= pjh_dt.f[k];
+    pi[k]->force.v_sig = vi_sig.f[k];
+    pj[k]->force.v_sig = vj_sig.f[k];
+    for (j = 0; j < 3; j++) {
+      pi[k]->a[j] -= pia[j].f[k];
+      pj[k]->a[j] += pja[j].f[k];
+    }
+  }
+
+#else
+
+  for (int k = 0; k < VEC_SIZE; k++)
+    runner_iact_force(R2[k], &Dx[3 * k], Hi[k], Hj[k], pi[k], pj[k]);
+
+#endif
+}
+
+/**
+ * @brief Force loop (non-symmetric version)
+ */
+
+__attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
+    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+
+  float r = sqrtf(r2), ri = 1.0f / r;
+  float xi, xj;
+  float hi_inv, hi2_inv;
+  float hj_inv, hj2_inv;
+  float wi, wj, wi_dx, wj_dx, wi_dr, wj_dr, w, dvdr;
+  float /*mi,*/ mj, POrho2i, POrho2j, rhoi, rhoj;
+  float v_sig, omega_ij, Pi_ij, alpha_ij, tc, v_sig_u;
+  float f;
+  int k;
+
+  /* Get some values in local variables. */
+  // mi = pi->mass;
+  mj = pj->mass;
+  rhoi = pi->rho;
+  rhoj = pj->rho;
+  POrho2i = pi->force.POrho2;
+  POrho2j = pj->force.POrho2;
+
+  /* Get the kernel for hi. */
+  hi_inv = 1.0f / hi;
+  hi2_inv = hi_inv * hi_inv;
+  xi = r * hi_inv;
+  kernel_deval(xi, &wi, &wi_dx);
+  wi_dr = hi2_inv * hi2_inv * wi_dx;
+
+  /* Get the kernel for hj. */
+  hj_inv = 1.0f / hj;
+  hj2_inv = hj_inv * hj_inv;
+  xj = r * hj_inv;
+  kernel_deval(xj, &wj, &wj_dx);
+  wj_dr = hj2_inv * hj2_inv * wj_dx;
+
+  /* Compute dv dot r. */
+  dvdr = (pi->v[0] - pj->v[0]) * dx[0] + (pi->v[1] - pj->v[1]) * dx[1] +
+         (pi->v[2] - pj->v[2]) * dx[2];
+  dvdr *= ri;
+
+  /* Compute the relative velocity. (This is 0 if the particles move away from
+   * each other and negative otherwise) */
+  omega_ij = fminf(dvdr, 0.f);
+
+  /* Compute signal velocity */
+  v_sig = pi->force.c + pj->force.c - 2.0f * omega_ij;
+
+  /* Compute viscosity parameter */
+  alpha_ij = -0.5f * (pi->alpha + pj->alpha);
+
+  /* Compute viscosity tensor */
+  Pi_ij = alpha_ij * v_sig * omega_ij / (rhoi + rhoj);
+
+  /* Apply balsara switch */
+  Pi_ij *= (pi->force.balsara + pj->force.balsara);
+
+  /* Thermal conductivity */
+  v_sig_u = sqrtf(2.f * (const_hydro_gamma - 1.f) *
+                  fabs(rhoi * pi->u - rhoj * pj->u) / (rhoi + rhoj));
+  tc = const_conductivity_alpha * v_sig_u / (rhoi + rhoj);
+  tc *= (wi_dr + wj_dr);
+
+  /* Get the common factor out. */
+  w = ri *
+      ((POrho2i * wi_dr + POrho2j * wj_dr) + 0.25f * Pi_ij * (wi_dr + wj_dr));
+
+  /* Use the force, Luke! */
+  for (k = 0; k < 3; k++) {
+    f = dx[k] * w;
+    pi->a_hydro[k] -= mj * f;
+  }
+
+  /* Get the time derivative for u. */
+  pi->force.u_dt +=
+      mj * dvdr * (POrho2i * wi_dr + 0.125f * Pi_ij * (wi_dr + wj_dr));
+
+  /* Add the thermal conductivity */
+  pi->force.u_dt += mj * tc * (pi->u - pj->u);
+
+  /* Get the time derivative for h. */
+  pi->h_dt -= mj * dvdr / rhoj * wi_dr;
+
+  /* Update the signal velocity. */
+  pi->force.v_sig = fmaxf(pi->force.v_sig, v_sig);
+  pj->force.v_sig = fmaxf(pj->force.v_sig, v_sig);
+}
+
+/**
+ * @brief Force loop (Vectorized non-symmetric version)
+ */
+
+__attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
+    float *R2, float *Dx, float *Hi, float *Hj, struct part **pi,
+    struct part **pj) {
+
+#ifdef VECTORIZE
+
+  vector r, r2, ri;
+  vector xi, xj;
+  vector hi, hj, hi_inv, hj_inv;
+  vector hi2_inv, hj2_inv;
+  vector wi, wj, wi_dx, wj_dx, wi_dr, wj_dr, dvdr;
+  vector w;
+  vector piPOrho2, pjPOrho2, pirho, pjrho, piu, pju;
+  vector mj;
+  vector f;
+  vector dx[3];
+  vector vi[3], vj[3];
+  vector pia[3];
+  vector piu_dt;
+  vector pih_dt;
+  vector ci, cj, v_sig, vi_sig, vj_sig;
+  vector omega_ij, Pi_ij, balsara;
+  vector pialpha, pjalpha, alpha_ij, v_sig_u, tc;
+  int j, k;
+
+/* Load stuff. */
+#if VEC_SIZE == 8
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass,
+                 pj[4]->mass, pj[5]->mass, pj[6]->mass, pj[7]->mass);
+  piPOrho2.v =
+      vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2, pi[2]->force.POrho2,
+              pi[3]->force.POrho2, pi[4]->force.POrho2, pi[5]->force.POrho2,
+              pi[6]->force.POrho2, pi[7]->force.POrho2);
+  pjPOrho2.v =
+      vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2, pj[2]->force.POrho2,
+              pj[3]->force.POrho2, pj[4]->force.POrho2, pj[5]->force.POrho2,
+              pj[6]->force.POrho2, pj[7]->force.POrho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho, pi[4]->rho,
+                    pi[5]->rho, pi[6]->rho, pi[7]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho, pj[4]->rho,
+                    pj[5]->rho, pj[6]->rho, pj[7]->rho);
+  piu.v = vec_set(pi[0]->u, pi[1]->u, pi[2]->u, pi[3]->u, pi[4]->u, pi[5]->u,
+                  pi[6]->u, pi[7]->u);
+  pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u, pj[4]->u, pj[5]->u,
+                  pj[6]->u, pj[7]->u);
+  ci.v =
+      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c,
+              pi[4]->force.c, pi[5]->force.c, pi[6]->force.c, pi[7]->force.c);
+  cj.v =
+      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c,
+              pj[4]->force.c, pj[5]->force.c, pj[6]->force.c, pj[7]->force.c);
+  vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
+                     pi[3]->force.v_sig, pi[4]->force.v_sig, pi[5]->force.v_sig,
+                     pi[6]->force.v_sig, pi[7]->force.v_sig);
+  vj_sig.v = vec_set(pj[0]->force.v_sig, pj[1]->force.v_sig, pj[2]->force.v_sig,
+                     pj[3]->force.v_sig, pj[4]->force.v_sig, pj[5]->force.v_sig,
+                     pj[6]->force.v_sig, pj[7]->force.v_sig);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k],
+                      pi[4]->v[k], pi[5]->v[k], pi[6]->v[k], pi[7]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k],
+                      pj[4]->v[k], pj[5]->v[k], pj[6]->v[k], pj[7]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k], Dx[12 + k],
+                      Dx[15 + k], Dx[18 + k], Dx[21 + k]);
+  balsara.v =
+      vec_set(pi[0]->force.balsara, pi[1]->force.balsara, pi[2]->force.balsara,
+              pi[3]->force.balsara, pi[4]->force.balsara, pi[5]->force.balsara,
+              pi[6]->force.balsara, pi[7]->force.balsara) +
+      vec_set(pj[0]->force.balsara, pj[1]->force.balsara, pj[2]->force.balsara,
+              pj[3]->force.balsara, pj[4]->force.balsara, pj[5]->force.balsara,
+              pj[6]->force.balsara, pj[7]->force.balsara);
+  pialpha.v = vec_set(pi[0]->alpha, pi[1]->alpha, pi[2]->alpha, pi[3]->alpha,
+                      pi[4]->alpha, pi[5]->alpha, pi[6]->alpha, pi[7]->alpha);
+  pjalpha.v = vec_set(pj[0]->alpha, pj[1]->alpha, pj[2]->alpha, pj[3]->alpha,
+                      pj[4]->alpha, pj[5]->alpha, pj[6]->alpha, pj[7]->alpha);
+#elif VEC_SIZE == 4
+  mj.v = vec_set(pj[0]->mass, pj[1]->mass, pj[2]->mass, pj[3]->mass);
+  piPOrho2.v = vec_set(pi[0]->force.POrho2, pi[1]->force.POrho2,
+                       pi[2]->force.POrho2, pi[3]->force.POrho2);
+  pjPOrho2.v = vec_set(pj[0]->force.POrho2, pj[1]->force.POrho2,
+                       pj[2]->force.POrho2, pj[3]->force.POrho2);
+  pirho.v = vec_set(pi[0]->rho, pi[1]->rho, pi[2]->rho, pi[3]->rho);
+  pjrho.v = vec_set(pj[0]->rho, pj[1]->rho, pj[2]->rho, pj[3]->rho);
+  piu.v = vec_set(pi[0]->u, pi[1]->u, pi[2]->u, pi[3]->u);
+  pju.v = vec_set(pj[0]->u, pj[1]->u, pj[2]->u, pj[3]->u);
+  ci.v =
+      vec_set(pi[0]->force.c, pi[1]->force.c, pi[2]->force.c, pi[3]->force.c);
+  cj.v =
+      vec_set(pj[0]->force.c, pj[1]->force.c, pj[2]->force.c, pj[3]->force.c);
+  vi_sig.v = vec_set(pi[0]->force.v_sig, pi[1]->force.v_sig, pi[2]->force.v_sig,
+                     pi[3]->force.v_sig);
+  vj_sig.v = vec_set(pj[0]->force.v_sig, pj[1]->force.v_sig, pj[2]->force.v_sig,
+                     pj[3]->force.v_sig);
+  for (k = 0; k < 3; k++) {
+    vi[k].v = vec_set(pi[0]->v[k], pi[1]->v[k], pi[2]->v[k], pi[3]->v[k]);
+    vj[k].v = vec_set(pj[0]->v[k], pj[1]->v[k], pj[2]->v[k], pj[3]->v[k]);
+  }
+  for (k = 0; k < 3; k++)
+    dx[k].v = vec_set(Dx[0 + k], Dx[3 + k], Dx[6 + k], Dx[9 + k]);
+  balsara.v = vec_set(pi[0]->force.balsara, pi[1]->force.balsara,
+                      pi[2]->force.balsara, pi[3]->force.balsara) +
+              vec_set(pj[0]->force.balsara, pj[1]->force.balsara,
+                      pj[2]->force.balsara, pj[3]->force.balsara);
+  pialpha.v = vec_set(pi[0]->alpha, pi[1]->alpha, pi[2]->alpha, pi[3]->alpha);
+  pjalpha.v = vec_set(pj[0]->alpha, pj[1]->alpha, pj[2]->alpha, pj[3]->alpha);
+#else
+#error
+#endif
+
+  /* Get the radius and inverse radius. */
+  r2.v = vec_load(R2);
+  ri.v = vec_rsqrt(r2.v);
+  ri.v = ri.v - vec_set1(0.5f) * ri.v * (r2.v * ri.v * ri.v - vec_set1(1.0f));
+  r.v = r2.v * ri.v;
+
+  /* Get the kernel for hi. */
+  hi.v = vec_load(Hi);
+  hi_inv.v = vec_rcp(hi.v);
+  hi_inv.v = hi_inv.v - hi_inv.v * (hi.v * hi_inv.v - vec_set1(1.0f));
+  hi2_inv.v = hi_inv.v * hi_inv.v;
+  xi.v = r.v * hi_inv.v;
+  kernel_deval_vec(&xi, &wi, &wi_dx);
+  wi_dr.v = hi2_inv.v * hi2_inv.v * wi_dx.v;
+
+  /* Get the kernel for hj. */
+  hj.v = vec_load(Hj);
+  hj_inv.v = vec_rcp(hj.v);
+  hj_inv.v = hj_inv.v - hj_inv.v * (hj.v * hj_inv.v - vec_set1(1.0f));
+  hj2_inv.v = hj_inv.v * hj_inv.v;
+  xj.v = r.v * hj_inv.v;
+  kernel_deval_vec(&xj, &wj, &wj_dx);
+  wj_dr.v = hj2_inv.v * hj2_inv.v * wj_dx.v;
+
+  /* Compute dv dot r. */
+  dvdr.v = ((vi[0].v - vj[0].v) * dx[0].v) + ((vi[1].v - vj[1].v) * dx[1].v) +
+           ((vi[2].v - vj[2].v) * dx[2].v);
+  dvdr.v = dvdr.v * ri.v;
+
+  /* Get the time derivative for h. */
+  pih_dt.v = mj.v / pjrho.v * dvdr.v * wi_dr.v;
+
+  /* Compute the relative velocity. (This is 0 if the particles move away from
+   * each other and negative otherwise) */
+  omega_ij.v = vec_fmin(dvdr.v, vec_set1(0.0f));
+
+  /* Compute signal velocity */
+  v_sig.v = ci.v + cj.v - vec_set1(2.0f) * omega_ij.v;
+
+  /* Compute viscosity parameter */
+  alpha_ij.v = vec_set1(-0.5f) * (pialpha.v + pjalpha.v);
+
+  /* Compute viscosity tensor */
+  Pi_ij.v = balsara.v * alpha_ij.v * v_sig.v * omega_ij.v / (pirho.v + pjrho.v);
+  Pi_ij.v *= (wi_dr.v + wj_dr.v);
+
+  /* Thermal conductivity */
+  v_sig_u.v = vec_sqrt(vec_set1(2.f * (const_hydro_gamma - 1.f)) *
+                       vec_fabs(pirho.v * piu.v - pjrho.v * pju.v) /
+                       (pirho.v + pjrho.v));
+  tc.v = vec_set1(const_conductivity_alpha) * v_sig_u.v / (pirho.v + pjrho.v);
+  tc.v *= (wi_dr.v + wj_dr.v);
+
+  /* Get the common factor out. */
+  w.v = ri.v * ((piPOrho2.v * wi_dr.v + pjPOrho2.v * wj_dr.v) +
+                vec_set1(0.25f) * Pi_ij.v);
+
+  /* Use the force, Luke! */
+  for (k = 0; k < 3; k++) {
+    f.v = dx[k].v * w.v;
+    pia[k].v = mj.v * f.v;
+  }
+
+  /* Get the time derivative for u. */
+  piu_dt.v =
+      mj.v * dvdr.v * (piPOrho2.v * wi_dr.v + vec_set1(0.125f) * Pi_ij.v);
+
+  /* Add the thermal conductivity */
+  piu_dt.v += mj.v * tc.v * (piu.v - pju.v);
+
+  /* compute the signal velocity (this is always symmetrical). */
+  vi_sig.v = vec_fmax(vi_sig.v, v_sig.v);
+  vj_sig.v = vec_fmax(vj_sig.v, v_sig.v);
+
+  /* Store the forces back on the particles. */
+  for (k = 0; k < VEC_SIZE; k++) {
+    pi[k]->force.u_dt += piu_dt.f[k];
+    pi[k]->h_dt -= pih_dt.f[k];
+    pi[k]->force.v_sig = vi_sig.f[k];
+    pj[k]->force.v_sig = vj_sig.f[k];
+    for (j = 0; j < 3; j++) pi[k]->a[j] -= pia[j].f[k];
+  }
+
+#else
+
+  for (int k = 0; k < VEC_SIZE; k++)
+    runner_iact_nonsym_force(R2[k], &Dx[3 * k], Hi[k], Hj[k], pi[k], pj[k]);
+
+#endif
+}
+
+#endif /* SWIFT_RUNNER_IACT_H */

src/hydro/Minimal/hydro_io.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Coypright (c) 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 <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+
+/**
+ * @brief Reads the different particles to the HDF5 file
+ *
+ * @param h_grp The HDF5 group in which to read the arrays.
+ * @param N The number of particles on that MPI rank.
+ * @param N_total The total number of particles (only used in MPI mode)
+ * @param offset The offset of the particles for this MPI rank (only used in MPI
+ *mode)
+ * @param parts The particle array
+ *
+ */
+__attribute__((always_inline)) INLINE static void hydro_read_particles(
+    hid_t h_grp, int N, long long N_total, long long offset,
+    struct part* parts) {
+
+  /* Read arrays */
+  readArray(h_grp, "Coordinates", DOUBLE, N, 3, parts, N_total, offset, x,
+            COMPULSORY);
+  readArray(h_grp, "Velocities", FLOAT, N, 3, parts, N_total, offset, v,
+            COMPULSORY);
+  readArray(h_grp, "Masses", FLOAT, N, 1, parts, N_total, offset, mass,
+            COMPULSORY);
+  readArray(h_grp, "SmoothingLength", FLOAT, N, 1, parts, N_total, offset, h,
+            COMPULSORY);
+  readArray(h_grp, "InternalEnergy", FLOAT, N, 1, parts, N_total, offset, u,
+            COMPULSORY);
+  readArray(h_grp, "ParticleIDs", ULONGLONG, N, 1, parts, N_total, offset, id,
+            COMPULSORY);
+  readArray(h_grp, "Acceleration", FLOAT, N, 3, parts, N_total, offset, a_hydro,
+            OPTIONAL);
+  readArray(h_grp, "Density", FLOAT, N, 1, parts, N_total, offset, rho,
+            OPTIONAL);
+}
+
+/**
+ * @brief Writes the different particles to the HDF5 file
+ *
+ * @param h_grp The HDF5 group in which to write the arrays.
+ * @param fileName The name of the file (unsued in MPI mode).
+ * @param xmfFile The XMF file to write to (unused in MPI mode).
+ * @param N The number of particles on that MPI rank.
+ * @param N_total The total number of particles (only used in MPI mode)
+ * @param mpi_rank The MPI rank of this node (only used in MPI mode)
+ * @param offset The offset of the particles for this MPI rank (only used in MPI
+ *mode)
+ * @param parts The particle array
+ * @param us The unit system to use
+ *
+ */
+__attribute__((always_inline)) INLINE static void hydro_write_particles(
+    hid_t h_grp, char* fileName, FILE* xmfFile, int N, long long N_total,
+    int mpi_rank, long long offset, struct part* parts, struct UnitSystem* us) {
+
+  /* Write arrays */
+  writeArray(h_grp, fileName, xmfFile, "Coordinates", DOUBLE, N, 3, parts,
+             N_total, mpi_rank, offset, x, us, UNIT_CONV_LENGTH);
+  writeArray(h_grp, fileName, xmfFile, "Velocities", FLOAT, N, 3, parts,
+             N_total, mpi_rank, offset, v, us, UNIT_CONV_SPEED);
+  writeArray(h_grp, fileName, xmfFile, "Masses", FLOAT, N, 1, parts, N_total,
+             mpi_rank, offset, mass, us, UNIT_CONV_MASS);
+  writeArray(h_grp, fileName, xmfFile, "SmoothingLength", FLOAT, N, 1, parts,
+             N_total, mpi_rank, offset, h, us, UNIT_CONV_LENGTH);
+  writeArray(h_grp, fileName, xmfFile, "InternalEnergy", FLOAT, N, 1, parts,
+             N_total, mpi_rank, offset, u, us, UNIT_CONV_ENERGY_PER_UNIT_MASS);
+  writeArray(h_grp, fileName, xmfFile, "ParticleIDs", ULONGLONG, N, 1, parts,
+             N_total, mpi_rank, offset, id, us, UNIT_CONV_NO_UNITS);
+  writeArray(h_grp, fileName, xmfFile, "Acceleration", FLOAT, N, 3, parts,
+             N_total, mpi_rank, offset, a_hydro, us, UNIT_CONV_ACCELERATION);
+  writeArray(h_grp, fileName, xmfFile, "Density", FLOAT, N, 1, parts, N_total,
+             mpi_rank, offset, rho, us, UNIT_CONV_DENSITY);
+}

src/hydro/Minimal/hydro_part.h

+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2012 Pedro Gonnet (pedro.gonnet@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 <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+
+/* Extra particle data not needed during the SPH loops over neighbours. */
+struct xpart {
+
+  /* Old position, at last tree rebuild. */
+  double x_old[3];
+
+  /* Velocity at the last full step. */
+  float v_full[3];
+
+  /* Old density. */
+  float omega;
+
+} __attribute__((aligned(xpart_align)));
+
+/* Data of a single particle. */
+struct part {
+
+  /* Particle position. */
+  double x[3];
+
+  /* Particle predicted velocity. */
+  float v[3];
+
+  /* Particle acceleration. */
+  float a_hydro[3];
+
+  /* Particle cutoff radius. */
+  float h;
+
+  /* Change in smoothing length over time. */
+  float h_dt;
+
+  /* Particle time of beginning of time-step. */
+  float t_begin;
+
+  /* Particle time of end of time-step. */
+  float t_end;
+
+  /* Particle internal energy. */
+  float u;
+
+  /* Particle density. */
+  float rho;
+
+  /* Derivative of the density with respect to this particle's smoothing length.
+   */
+  float rho_dh;
+
+  /* Particle viscosity parameter */
+  float alpha;
+
+  /* Store density/force specific stuff. */
+  // union {
+
+  struct {
+
+    /* Particle velocity divergence. */
+    float div_v;
+
+    /* Derivative of particle number density. */
+    float wcount_dh;
+
+    /* Particle velocity curl. */
+    float curl_v[3];
+
+    /* Particle number density. */
+    float wcount;
+
+  } density;
+
+  struct {
+
+    /* Balsara switch */
+    float balsara;
+
+    /* Aggregate quantities. */
+    float POrho2;
+
+    /* Change in particle energy over time. */
+    float u_dt;
+
+    /* Signal velocity */
+    float v_sig;
+
+    /* Sound speed */
+    float c;
+
+  } force;
+  //};
+
+  /* Particle mass. */
+  float mass;
+
+  /* Particle ID. */
+  unsigned long long id;
+
+  /* Pointer to corresponding gravity part. */
+  struct gpart* gpart;
+
+} __attribute__((aligned(part_align)));