Added cosmological factors to the Minimal SPH scheme.

src/hydro/Minimal/hydro.h

@@ -35,6 +35,7 @@
 
 #include "adiabatic_index.h"
 #include "approx_math.h"
+#include "cosmology.h"
 #include "dimension.h"
 #include "equation_of_state.h"
 #include "hydro_properties.h"
@@ -43,7 +44,7 @@
 #include "minmax.h"
 
 /**
- * @brief Returns the internal energy of a particle
+ * @brief Returns the comoving internal energy of a particle
  *
  * For implementations where the main thermodynamic variable
  * is not internal energy, this function computes the internal
@@ -51,25 +52,61 @@
  *
  * @param p The particle of interest
  */
-__attribute__((always_inline)) INLINE static float hydro_get_internal_energy(
-    const struct part *restrict p) {
+__attribute__((always_inline)) INLINE static float
+hydro_get_comoving_internal_energy(const struct part *restrict p) {
 
   return p->u;
 }
 
 /**
- * @brief Returns the pressure of a particle
+ * @brief Returns the physical internal energy of a particle
+ *
+ * For implementations where the main thermodynamic variable
+ * is not internal energy, this function computes the internal
+ * energy from the thermodynamic variable and converts it to
+ * physical coordinates.
+ *
+ * @param p The particle of interest.
+ * @param cosmo The cosmological model.
+ */
+__attribute__((always_inline)) INLINE static float
+hydro_get_physical_internal_energy(const struct part *restrict p,
+                                   const struct cosmology *cosmo) {
+
+  return p->u * cosmo->a_factor_internal_energy;
+}
+
+/**
+ * @brief Returns the comoving pressure of a particle
+ *
+ * Computes the pressure based on the particle's properties.
  *
  * @param p The particle of interest
  */
-__attribute__((always_inline)) INLINE static float hydro_get_pressure(
+__attribute__((always_inline)) INLINE static float hydro_get_comoving_pressure(
     const struct part *restrict p) {
 
   return gas_pressure_from_internal_energy(p->rho, p->u);
 }
 
 /**
- * @brief Returns the entropy of a particle
+ * @brief Returns the physical pressure of a particle
+ *
+ * Computes the pressure based on the particle's properties and
+ * convert it to physical coordinates.
+ *
+ * @param p The particle of interest
+ * @param cosmo The cosmological model.
+ */
+__attribute__((always_inline)) INLINE static float hydro_get_physical_pressure(
+    const struct part *restrict p, const struct cosmology *cosmo) {
+
+  return cosmo->a_factor_pressure *
+         gas_pressure_from_internal_energy(p->rho, p->u);
+}
+
+/**
+ * @brief Returns the comoving entropy of a particle
  *
  * For implementations where the main thermodynamic variable
  * is not entropy, this function computes the entropy from
@@ -77,34 +114,78 @@ __attribute__((always_inline)) INLINE static float hydro_get_pressure(
  *
  * @param p The particle of interest
  */
-__attribute__((always_inline)) INLINE static float hydro_get_entropy(
+__attribute__((always_inline)) INLINE static float hydro_get_comoving_entropy(
     const struct part *restrict p) {
 
   return gas_entropy_from_internal_energy(p->rho, p->u);
 }
 
 /**
- * @brief Returns the sound speed of a particle
+ * @brief Returns the physical entropy of a particle
+ *
+ * For implementations where the main thermodynamic variable
+ * is not entropy, this function computes the entropy from
+ * the thermodynamic variable and converts it to
+ * physical coordinates.
  *
  * @param p The particle of interest
+ * @param cosmo The cosmological model.
  */
-__attribute__((always_inline)) INLINE static float hydro_get_soundspeed(
-    const struct part *restrict p) {
+__attribute__((always_inline)) INLINE static float hydro_get_physical_entropy(
+    const struct part *restrict p, const struct cosmology *cosmo) {
+
+  /* Note: no cosmological conversion required here with our choice of
+   * coordinates. */
+  return gas_entropy_from_internal_energy(p->rho, p->u);
+}
+
+/**
+ * @brief Returns the comoving sound speed of a particle
+ *
+ * @param p The particle of interest
+ */
+__attribute__((always_inline)) INLINE static float
+hydro_get_comoving_soundspeed(const struct part *restrict p) {
 
   return p->force.soundspeed;
 }
 
 /**
- * @brief Returns the density of a particle
+ * @brief Returns the physical sound speed of a particle
  *
  * @param p The particle of interest
+ * @param cosmo The cosmological model.
  */
-__attribute__((always_inline)) INLINE static float hydro_get_density(
+__attribute__((always_inline)) INLINE static float
+hydro_get_physical_soundspeed(const struct part *restrict p,
+                              const struct cosmology *cosmo) {
+
+  return cosmo->a_factor_sound_speed * p->force.soundspeed;
+}
+
+/**
+ * @brief Returns the comoving density of a particle
+ *
+ * @param p The particle of interest
+ */
+__attribute__((always_inline)) INLINE static float hydro_get_comoving_density(
     const struct part *restrict p) {
 
   return p->rho;
 }
 
+/**
+ * @brief Returns the comoving density of a particle.
+ *
+ * @param p The particle of interest
+ * @param cosmo The cosmological model.
+ */
+__attribute__((always_inline)) INLINE static float hydro_get_physical_density(
+    const struct part *restrict p, const struct cosmology *cosmo) {
+
+  return cosmo->a3_inv * p->rho;
+}
+
 /**
  * @brief Returns the mass of a particle
  *
@@ -121,16 +202,20 @@ __attribute__((always_inline)) INLINE static float hydro_get_mass(
  *
  * @param p The particle of interest
  * @param xp The extended data of the particle.
- * @param dt The time since the last kick.
+ * @param dt_kick_hydro The time (for hydro accelerations) since the last kick.
+ * @param dt_kick_grav The time (for gravity accelerations) since the last kick.
  * @param v (return) The velocities at the current time.
  */
 __attribute__((always_inline)) INLINE static void hydro_get_drifted_velocities(
-    const struct part *restrict p, const struct xpart *xp, float dt,
-    float v[3]) {
-
-  v[0] = xp->v_full[0] + p->a_hydro[0] * dt;
-  v[1] = xp->v_full[1] + p->a_hydro[1] * dt;
-  v[2] = xp->v_full[2] + p->a_hydro[2] * dt;
+    const struct part *restrict p, const struct xpart *xp, float dt_kick_hydro,
+    float dt_kick_grav, float v[3]) {
+
+  v[0] = xp->v_full[0] + p->a_hydro[0] * dt_kick_hydro +
+         xp->a_grav[0] * dt_kick_grav;
+  v[1] = xp->v_full[1] + p->a_hydro[1] * dt_kick_hydro +
+         xp->a_grav[1] * dt_kick_grav;
+  v[2] = xp->v_full[2] + p->a_hydro[2] * dt_kick_hydro +
+         xp->a_grav[2] * dt_kick_grav;
 }
 
 /**
@@ -168,17 +253,18 @@ __attribute__((always_inline)) INLINE static void hydro_set_internal_energy_dt(
  * @param p Pointer to the particle data
  * @param xp Pointer to the extended particle data
  * @param hydro_properties The SPH parameters
- *
+ * @param cosmo The cosmological model.
  */
 __attribute__((always_inline)) INLINE static float hydro_compute_timestep(
     const struct part *restrict p, const struct xpart *restrict xp,
-    const struct hydro_props *restrict hydro_properties) {
+    const struct hydro_props *restrict hydro_properties,
+    const struct cosmology *restrict cosmo) {
 
   const float CFL_condition = hydro_properties->CFL_condition;
 
   /* CFL condition */
-  const float dt_cfl =
-      2.f * kernel_gamma * CFL_condition * p->h / p->force.v_sig;
+  const float dt_cfl = 2.f * kernel_gamma * CFL_condition * cosmo->a * p->h /
+                       (cosmo->a_factor_sound_speed * p->force.v_sig);
 
   return dt_cfl;
 }
@@ -218,13 +304,15 @@ __attribute__((always_inline)) INLINE static void hydro_init_part(
  * Multiplies the density and number of neighbours by the appropiate constants
  * and add the self-contribution term.
  * Additional quantities such as velocity gradients will also get the final
- *terms
- * added to them here.
+ * terms added to them here.
+ *
+ * Also adds/multiplies the cosmological terms if need be.
  *
  * @param p The particle to act upon
+ * @param cosmo The cosmological model.
  */
 __attribute__((always_inline)) INLINE static void hydro_end_density(
-    struct part *restrict p) {
+    struct part *restrict p, const struct cosmology *cosmo) {
 
   /* Some smoothing length multiples. */
   const float h = p->h;
@@ -248,11 +336,17 @@ __attribute__((always_inline)) INLINE static void hydro_end_density(
 /**
  * @brief Sets all particle fields to sensible values when the #part has 0 ngbs.
  *
+ * In the desperate case where a particle has no neighbours (likely because
+ * of the h_max ceiling), set the particle fields to something sensible to avoid
+ * NaNs in the next calculations.
+ *
  * @param p The particle to act upon
  * @param xp The extended particle data to act upon
+ * @param cosmo The cosmological model.
  */
 __attribute__((always_inline)) INLINE static void hydro_part_has_no_neighbours(
-    struct part *restrict p, struct xpart *restrict xp) {
+    struct part *restrict p, struct xpart *restrict xp,
+    const struct cosmology *cosmo) {
 
   /* Some smoothing length multiples. */
   const float h = p->h;
@@ -278,9 +372,11 @@ __attribute__((always_inline)) INLINE static void hydro_part_has_no_neighbours(
  *
  * @param p The particle to act upon
  * @param xp The extended particle data to act upon
+ * @param cosmo The current cosmological model.
  */
 __attribute__((always_inline)) INLINE static void hydro_prepare_force(
-    struct part *restrict p, struct xpart *restrict xp) {
+    struct part *restrict p, struct xpart *restrict xp,
+    const struct cosmology *cosmo) {
 
   /* Compute the pressure */
   const float pressure = gas_pressure_from_internal_energy(p->rho, p->u);
@@ -346,17 +442,22 @@ __attribute__((always_inline)) INLINE static void hydro_reset_predicted_values(
  * Additional hydrodynamic quantites are drifted forward in time here. These
  * include thermal quantities (thermal energy or total energy or entropy, ...).
  *
+ * Note the different time-step sizes used for the different quantities as they
+ * include cosmological factors.
+ *
  * @param p The particle.
  * @param xp The extended data of the particle.
- * @param dt The drift time-step.
+ * @param dt_drift The drift time-step for positions.
+ * @param dt_therm The drift time-step for thermal quantities.
  */
 __attribute__((always_inline)) INLINE static void hydro_predict_extra(
-    struct part *restrict p, const struct xpart *restrict xp, float dt) {
+    struct part *restrict p, const struct xpart *restrict xp, float dt_drift,
+    float dt_therm) {
 
   const float h_inv = 1.f / p->h;
 
   /* Predict smoothing length */
-  const float w1 = p->force.h_dt * h_inv * dt;
+  const float w1 = p->force.h_dt * h_inv * dt_drift;
   if (fabsf(w1) < 0.2f)
     p->h *= approx_expf(w1); /* 4th order expansion of exp(w) */
   else
@@ -370,7 +471,7 @@ __attribute__((always_inline)) INLINE static void hydro_predict_extra(
     p->rho *= expf(w2);
 
   /* Predict the internal energy */
-  p->u += p->u_dt * dt;
+  p->u += p->u_dt * dt_therm;
 
   /* Compute the new pressure */
   const float pressure = gas_pressure_from_internal_energy(p->rho, p->u);
@@ -386,13 +487,16 @@ __attribute__((always_inline)) INLINE static void hydro_predict_extra(
  * @brief Finishes the force calculation.
  *
  * Multiplies the force and accelerations by the appropiate constants
- * and add the self-contribution term. In most cases, there is nothing
+ * and add the self-contribution term. In most cases, there is little
  * to do here.
  *
+ * Cosmological terms are also added/multiplied here.
+ *
  * @param p The particle to act upon
+ * @param cosmo The current cosmological model.
  */
 __attribute__((always_inline)) INLINE static void hydro_end_force(
-    struct part *restrict p) {
+    struct part *restrict p, const struct cosmology *cosmo) {
 
   p->force.h_dt *= p->h * hydro_dimension_inv;
 }
@@ -403,18 +507,18 @@ __attribute__((always_inline)) INLINE static void hydro_end_force(
  * Additional hydrodynamic quantites are kicked forward in time here. These
  * include thermal quantities (thermal energy or total energy or entropy, ...).
  *
- * @param p The particle to act upon
- * @param xp The particle extended data to act upon
- * @param dt The time-step for this kick
+ * @param p The particle to act upon.
+ * @param xp The particle extended data to act upon.
+ * @param dt_therm The time-step for this kick (for thermodynamic quantities).
  */
 __attribute__((always_inline)) INLINE static void hydro_kick_extra(
-    struct part *restrict p, struct xpart *restrict xp, float dt) {
+    struct part *restrict p, struct xpart *restrict xp, float dt_therm) {
 
   /* Do not decrease the energy by more than a factor of 2*/
-  if (dt > 0. && p->u_dt * dt < -0.5f * xp->u_full) {
-    p->u_dt = -0.5f * xp->u_full / dt;
+  if (dt_therm > 0. && p->u_dt * dt_therm < -0.5f * xp->u_full) {
+    p->u_dt = -0.5f * xp->u_full / dt_therm;
   }
-  xp->u_full += p->u_dt * dt;
+  xp->u_full += p->u_dt * dt_therm;
 
   /* Compute the pressure */
   const float pressure = gas_pressure_from_internal_energy(p->rho, xp->u_full);

src/hydro/Minimal/hydro_debug.h

@@ -43,8 +43,9 @@ __attribute__((always_inline)) INLINE static void hydro_debug_particle(
       "time_bin=%d\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->u, p->u_dt, p->force.v_sig, p->force.pressure, p->h, p->force.h_dt,
-      (int)p->density.wcount, p->mass, p->density.rho_dh, p->rho, p->time_bin);
+      p->u, p->u_dt, p->force.v_sig, hydro_get_comoving_pressure(p), p->h,
+      p->force.h_dt, (int)p->density.wcount, p->mass, p->density.rho_dh, p->rho,
+      p->time_bin);
 }
 
 #endif /* SWIFT_MINIMAL_HYDRO_DEBUG_H */

src/hydro/Minimal/hydro_iact.h

@@ -36,10 +36,20 @@
 #include "minmax.h"
 
 /**
- * @brief Density loop
+ * @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(
-    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+    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;
 
@@ -71,10 +81,20 @@ __attribute__((always_inline)) INLINE static void runner_iact_density(
 }
 
 /**
- * @brief Density loop (non-symmetric version)
+ * @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(
-    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+    float r2, const float *dx, float hi, float hj, struct part *restrict pi,
+    const struct part *restrict pj, float a, float H) {
 
   float wi, wi_dx;
 
@@ -95,12 +115,24 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_density(
 }
 
 /**
- * @brief Force loop
+ * @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(
-    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+    float r2, const float *dx, float hi, float hj, struct part *restrict pi,
+    struct part *restrict pj, float a, float H) {
 
-  const float fac_mu = 1.f; /* Will change with cosmological integration */
+  /* Cosmological factors entering the EoMs */
+  const float fac_mu = pow_three_gamma_minus_five_over_two(a);
+  const float a2_Hubble = a * a * H;
 
   const float r = sqrtf(r2);
   const float r_inv = 1.0f / r;
@@ -136,7 +168,7 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
   /* Compute dv dot r. */
   const float 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];
+                     (pi->v[2] - pj->v[2]) * dx[2] + a2_Hubble * r2;
 
   /* Are the particles moving towards each others ? */
   const float omega_ij = min(dvdr, 0.f);
@@ -195,12 +227,24 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
 }
 
 /**
- * @brief Force loop (non-symmetric version)
+ * @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(
-    float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
+    float r2, const float *dx, float hi, float hj, struct part *restrict pi,
+    const struct part *restrict pj, float a, float H) {
 
-  const float fac_mu = 1.f; /* Will change with cosmological integration */
+  /* Cosmological factors entering the EoMs */
+  const float fac_mu = pow_three_gamma_minus_five_over_two(a);
+  const float a2_Hubble = a * a * H;
 
   const float r = sqrtf(r2);
   const float r_inv = 1.0f / r;
@@ -236,7 +280,7 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
   /* Compute dv dot r. */
   const float 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];
+                     (pi->v[2] - pj->v[2]) * dx[2] + a2_Hubble * r2;
 
   /* Are the particles moving towards each others ? */
   const float omega_ij = min(dvdr, 0.f);

src/hydro/Minimal/hydro_io.h

@@ -71,12 +71,12 @@ void hydro_read_particles(struct part* parts, struct io_props* list,
 
 void convert_S(const struct engine* e, const struct part* p, float* ret) {
 
-  ret[0] = hydro_get_entropy(p);
+  ret[0] = hydro_get_comoving_entropy(p);
 }
 
 void convert_P(const struct engine* e, const struct part* p, float* ret) {
 
-  ret[0] = hydro_get_pressure(p);
+  ret[0] = hydro_get_comoving_pressure(p);
 }
 
 void convert_part_pos(const struct engine* e, const struct part* p,

src/hydro/Minimal/hydro_part.h

@@ -53,6 +53,9 @@ struct xpart {
   /*! Velocity at the last full step. */
   float v_full[3];
 
+  /*! Gravitational acceleration at the last full step. */
+  float a_grav[3];
+
   /*! Internal energy at the last full step. */
   float u_full;