Merge branch 'fix_minimal_sph' into 'master'

Fix the minimal version of SPH

Ok, I have now fixed the minimalistic implementation of SPH. That's the one that should be used as a template for other people to implement their stuff. It's overly documented and now works on all the test-cases we have in the examples directory.  

Don't know if you want to look at this or not @pdraper given that it does not affect our default setup at all.

Solves #148.

See merge request !218

src/hydro/Gadget2/hydro_io.h

@@ -107,9 +107,10 @@ void writeSPHflavour(hid_t h_grpsph) {
 
   /* Viscosity and thermal conduction */
   writeAttribute_s(h_grpsph, "Thermal Conductivity Model",
-                   "(No treatment) Legacy Gadget-2 as in Springel (2005)");
-  writeAttribute_s(h_grpsph, "Viscosity Model",
-                   "Legacy Gadget-2 as in Springel (2005)");
+                   "(No treatment) as in Springel (2005)");
+  writeAttribute_s(
+      h_grpsph, "Viscosity Model",
+      "as in Springel (2005), i.e. Monaghan (1992) with Balsara (1995) switch");
   writeAttribute_f(h_grpsph, "Viscosity alpha", const_viscosity_alpha);
   writeAttribute_f(h_grpsph, "Viscosity beta", 3.f);
 }

src/hydro/Minimal/hydro.h

@@ -16,10 +16,29 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  ******************************************************************************/
+#ifndef SWIFT_MINIMAL_HYDRO_H
+#define SWIFT_MINIMAL_HYDRO_H
+
+/**
+ * @file Minimal/hydro.h
+ * @brief Minimal conservative implementation of SPH (Non-neighbour loop
+ * equations)
+ *
+ * The thermal variable is the internal energy (u). Simple constant
+ * viscosity term without switches is implemented. No thermal conduction
+ * term is implemented.
+ *
+ * This corresponds to equations (43), (44), (45), (101), (103)  and (104) with
+ * \f$\beta=3\f$ and \f$\alpha_u=0\f$ of
+ * Price, D., Journal of Computational Physics, 2012, Volume 231, Issue 3,
+ * pp. 759-794.
+ */
 
 #include "adiabatic_index.h"
-#include "approx_math.h"
+#include "dimension.h"
 #include "equation_of_state.h"
+#include "hydro_properties.h"
+#include "kernel_hydro.h"
 
 /**
  * @brief Returns the internal energy of a particle
@@ -34,7 +53,7 @@
 __attribute__((always_inline)) INLINE static float hydro_get_internal_energy(
     const struct part *restrict p, float dt) {
 
-  return p->u;
+  return p->u + p->u_dt * dt;
 }
 
 /**
@@ -46,7 +65,9 @@ __attribute__((always_inline)) INLINE static float hydro_get_internal_energy(
 __attribute__((always_inline)) INLINE static float hydro_get_pressure(
     const struct part *restrict p, float dt) {
 
-  return gas_pressure_from_internal_energy(p->rho, p->u);
+  const float u = p->u + p->u_dt * dt;
+
+  return gas_pressure_from_internal_energy(p->rho, u);
 }
 
 /**
@@ -62,7 +83,9 @@ __attribute__((always_inline)) INLINE static float hydro_get_pressure(
 __attribute__((always_inline)) INLINE static float hydro_get_entropy(
     const struct part *restrict p, float dt) {
 
-  return gas_entropy_from_internal_energy(p->rho, p->u);
+  const float u = p->u + p->u_dt * dt;
+
+  return gas_entropy_from_internal_energy(p->rho, u);
 }
 
 /**
@@ -74,7 +97,9 @@ __attribute__((always_inline)) INLINE static float hydro_get_entropy(
 __attribute__((always_inline)) INLINE static float hydro_get_soundspeed(
     const struct part *restrict p, float dt) {
 
-  return gas_soundspeed_from_internal_energy(p->rho, p->u);
+  const float u = p->u + p->u_dt * dt;
+
+  return gas_soundspeed_from_internal_energy(p->rho, u);
 }
 
 /**
@@ -150,7 +175,6 @@ __attribute__((always_inline)) INLINE static void hydro_first_init_part(
   xp->v_full[0] = p->v[0];
   xp->v_full[1] = p->v[1];
   xp->v_full[2] = p->v[2];
-  xp->u_full = p->u;
 }
 
 /**
@@ -164,6 +188,7 @@ __attribute__((always_inline)) INLINE static void hydro_first_init_part(
  */
 __attribute__((always_inline)) INLINE static void hydro_init_part(
     struct part *restrict p) {
+
   p->density.wcount = 0.f;
   p->density.wcount_dh = 0.f;
   p->rho = 0.f;
@@ -227,7 +252,10 @@ __attribute__((always_inline)) INLINE static void hydro_prepare_force(
     struct part *restrict p, struct xpart *restrict xp, int ti_current,
     double timeBase) {
 
-  p->force.pressure = p->rho * p->u * hydro_gamma_minus_one;
+  const float half_dt = (ti_current - (p->ti_begin + p->ti_end) / 2) * timeBase;
+  const float pressure = hydro_get_pressure(p, half_dt);
+
+  p->force.pressure = pressure;
 }
 
 /**
@@ -268,10 +296,9 @@ __attribute__((always_inline)) INLINE static void hydro_predict_extra(
     struct part *restrict p, const struct xpart *restrict xp, int t0, int t1,
     double timeBase) {
 
-  p->u = xp->u_full;
-
-  /* Need to recompute the pressure as well */
-  p->force.pressure = p->rho * p->u * hydro_gamma_minus_one;
+  /* Drift the pressure */
+  const float dt_entr = (t1 - (p->ti_begin + p->ti_end) / 2) * timeBase;
+  p->force.pressure = hydro_get_pressure(p, dt_entr);
 }
 
 /**
@@ -304,11 +331,15 @@ __attribute__((always_inline)) INLINE static void hydro_kick_extra(
     struct part *restrict p, struct xpart *restrict xp, float dt,
     float half_dt) {
 
-  /* Kick in momentum space */
-  xp->u_full += p->u_dt * dt;
+  /* Do not decrease the energy by more than a factor of 2*/
+  const float u_change = p->u_dt * dt;
+  if (u_change > -0.5f * p->u)
+    p->u += u_change;
+  else
+    p->u *= 0.5f;
 
-  /* Get the predicted internal energy */
-  p->u = xp->u_full - half_dt * p->u_dt;
+  /* Do not 'overcool' when timestep increases */
+  if (p->u + p->u_dt * half_dt < 0.5f * p->u) p->u_dt = -0.5f * p->u / half_dt;
 }
 
 /**
@@ -323,3 +354,5 @@ __attribute__((always_inline)) INLINE static void hydro_kick_extra(
  */
 __attribute__((always_inline)) INLINE static void hydro_convert_quantities(
     struct part *restrict p) {}
+
+#endif /* SWIFT_MINIMAL_HYDRO_H */

src/hydro/Minimal/hydro_debug.h

@@ -16,18 +16,36 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  ******************************************************************************/
+#ifndef SWIFT_MINIMAL_HYDRO_DEBUG_H
+#define SWIFT_MINIMAL_HYDRO_DEBUG_H
+
+/**
+ * @file Minimal/hydro_debug.h
+ * @brief Minimal conservative implementation of SPH (Debugging routines)
+ *
+ * The thermal variable is the internal energy (u). Simple constant
+ * viscosity term without switches is implemented. No thermal conduction
+ * term is implemented.
+ *
+ * This corresponds to equations (43), (44), (45), (101), (103)  and (104) with
+ * \f$\beta=3\f$ and \f$\alpha_u=0\f$ of
+ * Price, D., Journal of Computational Physics, 2012, Volume 231, Issue 3,
+ * pp. 759-794.
+ */
 
 __attribute__((always_inline)) INLINE static void hydro_debug_particle(
     const struct part* p, const struct xpart* xp) {
   printf(
       "x=[%.3e,%.3e,%.3e], "
       "v=[%.3e,%.3e,%.3e],v_full=[%.3e,%.3e,%.3e] \n a=[%.3e,%.3e,%.3e], "
-      "u_full=%.3e, u=%.3e, du/dt=%.3e v_sig=%.3e, P=%.3e\n"
-      "h=%.3e, dh/dt=%.3e "
-      "wcount=%d, m=%.3e, dh_drho=%.3e, rho=%.3e, t_begin=%d, t_end=%d\n",
+      "u=%.3e, du/dt=%.3e v_sig=%.3e, P=%.3e\n"
+      "h=%.3e, dh/dt=%.3e wcount=%d, m=%.3e, dh_drho=%.3e, rho=%.3e, "
+      "t_begin=%d, t_end=%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],
-      xp->u_full, 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->rho_dh, p->rho,
-      p->ti_begin, p->ti_end);
+      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->rho_dh, p->rho, p->ti_begin,
+      p->ti_end);
 }
+
+#endif /* SWIFT_MINIMAL_HYDRO_DEBUG_H */

src/hydro/Minimal/hydro_iact.h

@@ -16,18 +16,25 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  ******************************************************************************/
-#ifndef SWIFT_RUNNER_IACT_MINIMAL_H
-#define SWIFT_RUNNER_IACT_MINIMAL_H
-
-#include "adiabatic_index.h"
+#ifndef SWIFT_MINIMAL_HYDRO_IACT_H
+#define SWIFT_MINIMAL_HYDRO_IACT_H
 
 /**
- * @brief Minimal conservative implementation of SPH
+ * @file Minimal/hydro_iact.h
+ * @brief Minimal conservative implementation of SPH (Neighbour loop equations)
+ *
+ * The thermal variable is the internal energy (u). Simple constant
+ * viscosity term without switches is implemented. No thermal conduction
+ * term is implemented.
  *
- * The thermal variable is the internal energy (u). No viscosity nor
- * thermal conduction terms are implemented.
+ * This corresponds to equations (43), (44), (45), (101), (103)  and (104) with
+ * \f$\beta=3\f$ and \f$\alpha_u=0\f$ of
+ * Price, D., Journal of Computational Physics, 2012, Volume 231, Issue 3,
+ * pp. 759-794.
  */
 
+#include "adiabatic_index.h"
+
 /**
  * @brief Density loop
  */
@@ -115,6 +122,8 @@ runner_iact_nonsym_vec_density(float *R2, float *Dx, float *Hi, float *Hj,
 __attribute__((always_inline)) INLINE static void runner_iact_force(
     float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
 
+  const float fac_mu = 1.f; /* Will change with cosmological integration */
+
   const float r = sqrtf(r2);
   const float r_inv = 1.0f / r;
 
@@ -143,34 +152,60 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
   const float wj_dr = hjd_inv * wj_dx;
 
   /* Compute gradient terms */
-  const float P_over_rho_i = pressurei / (rhoi * rhoi) * pi->rho_dh;
-  const float P_over_rho_j = pressurej / (rhoj * rhoj) * pj->rho_dh;
+  const float P_over_rho2_i = pressurei / (rhoi * rhoi) * pi->rho_dh;
+  const float P_over_rho2_j = pressurej / (rhoj * rhoj) * pj->rho_dh;
 
   /* 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];
 
-  /* Compute sound speeds */
+  /* Are the particles moving towards each others ? */
+  const float omega_ij = fminf(dvdr, 0.f);
+  const float mu_ij = fac_mu * r_inv * omega_ij; /* This is 0 or negative */
+
+  /* Compute sound speeds and signal velocity */
   const float ci = sqrtf(hydro_gamma * pressurei / rhoi);
   const float cj = sqrtf(hydro_gamma * pressurej / rhoj);
-  const float v_sig = ci + cj;
+  const float v_sig = ci + cj - 3.f * mu_ij;
+
+  /* Construct the full viscosity term */
+  const float rho_ij = 0.5f * (rhoi + rhoj);
+  const float visc = -0.5f * const_viscosity_alpha * v_sig * mu_ij / rho_ij;
+
+  /* Convolve with the kernel */
+  const float visc_acc_term = 0.5f * visc * (wi_dr + wj_dr) * r_inv;
 
   /* SPH acceleration term */
-  const float sph_term = (P_over_rho_i * wi_dr + P_over_rho_j * wj_dr) * r_inv;
+  const float sph_acc_term =
+      (P_over_rho2_i * wi_dr + P_over_rho2_j * wj_dr) * r_inv;
+
+  /* Assemble the acceleration */
+  const float acc = sph_acc_term + visc_acc_term;
 
   /* Use the force Luke ! */
-  pi->a_hydro[0] -= mj * sph_term * dx[0];
-  pi->a_hydro[1] -= mj * sph_term * dx[1];
-  pi->a_hydro[2] -= mj * sph_term * dx[2];
+  pi->a_hydro[0] -= mj * acc * dx[0];
+  pi->a_hydro[1] -= mj * acc * dx[1];
+  pi->a_hydro[2] -= mj * acc * dx[2];
 
-  pj->a_hydro[0] += mi * sph_term * dx[0];
-  pj->a_hydro[1] += mi * sph_term * dx[1];
-  pj->a_hydro[2] += mi * sph_term * dx[2];
+  pj->a_hydro[0] += mi * acc * dx[0];
+  pj->a_hydro[1] += mi * acc * dx[1];
+  pj->a_hydro[2] += mi * acc * dx[2];
 
   /* Get the time derivative for u. */
-  pi->u_dt += P_over_rho_i * mj * dvdr * r_inv * wi_dr;
-  pj->u_dt += P_over_rho_j * mi * dvdr * r_inv * wj_dr;
+  const float sph_du_term_i = P_over_rho2_i * dvdr * r_inv * wi_dr;
+  const float sph_du_term_j = P_over_rho2_j * dvdr * r_inv * wj_dr;
+
+  /* Viscosity term */
+  const float visc_du_term = 0.5f * visc_acc_term * dvdr;
+
+  /* Assemble the energy equation term */
+  const float du_dt_i = sph_du_term_i + visc_du_term;
+  const float du_dt_j = sph_du_term_j + visc_du_term;
+
+  /* Internal energy time derivatibe */
+  pi->u_dt += du_dt_i * mj;
+  pj->u_dt += du_dt_j * mi;
 
   /* Get the time derivative for h. */
   pi->force.h_dt -= mj * dvdr * r_inv / rhoj * wi_dr;
@@ -198,6 +233,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_vec_force(
 __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
     float r2, float *dx, float hi, float hj, struct part *pi, struct part *pj) {
 
+  const float fac_mu = 1.f; /* Will change with cosmological integration */
+
   const float r = sqrtf(r2);
   const float r_inv = 1.0f / r;
 
@@ -226,29 +263,53 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
   const float wj_dr = hjd_inv * wj_dx;
 
   /* Compute gradient terms */
-  const float P_over_rho_i = pressurei / (rhoi * rhoi) * pi->rho_dh;
-  const float P_over_rho_j = pressurej / (rhoj * rhoj) * pj->rho_dh;
+  const float P_over_rho2_i = pressurei / (rhoi * rhoi) * pi->rho_dh;
+  const float P_over_rho2_j = pressurej / (rhoj * rhoj) * pj->rho_dh;
 
   /* 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];
 
-  /* Compute sound speeds */
+  /* Are the particles moving towards each others ? */
+  const float omega_ij = fminf(dvdr, 0.f);
+  const float mu_ij = fac_mu * r_inv * omega_ij; /* This is 0 or negative */
+
+  /* Compute sound speeds and signal velocity */
   const float ci = sqrtf(hydro_gamma * pressurei / rhoi);
   const float cj = sqrtf(hydro_gamma * pressurej / rhoj);
-  const float v_sig = ci + cj;
+  const float v_sig = ci + cj - 3.f * mu_ij;
+
+  /* Construct the full viscosity term */
+  const float rho_ij = 0.5f * (rhoi + rhoj);
+  const float visc = -0.5f * const_viscosity_alpha * v_sig * mu_ij / rho_ij;
+
+  /* Convolve with the kernel */
+  const float visc_acc_term = 0.5f * visc * (wi_dr + wj_dr) * r_inv;
 
   /* SPH acceleration term */
-  const float sph_term = (P_over_rho_i * wi_dr + P_over_rho_j * wj_dr) * r_inv;
+  const float sph_acc_term =
+      (P_over_rho2_i * wi_dr + P_over_rho2_j * wj_dr) * r_inv;
+
+  /* Assemble the acceleration */
+  const float acc = sph_acc_term + visc_acc_term;
 
   /* Use the force Luke ! */
-  pi->a_hydro[0] -= mj * sph_term * dx[0];
-  pi->a_hydro[1] -= mj * sph_term * dx[1];
-  pi->a_hydro[2] -= mj * sph_term * dx[2];
+  pi->a_hydro[0] -= mj * acc * dx[0];
+  pi->a_hydro[1] -= mj * acc * dx[1];
+  pi->a_hydro[2] -= mj * acc * dx[2];
 
   /* Get the time derivative for u. */
-  pi->u_dt += P_over_rho_i * mj * dvdr * r_inv * wi_dr;
+  const float sph_du_term_i = P_over_rho2_i * dvdr * r_inv * wi_dr;
+
+  /* Viscosity term */
+  const float visc_du_term = 0.5f * visc_acc_term * dvdr;
+
+  /* Assemble the energy equation term */
+  const float du_dt_i = sph_du_term_i + visc_du_term;
+
+  /* Internal energy time derivatibe */
+  pi->u_dt += du_dt_i * mj;
 
   /* Get the time derivative for h. */
   pi->force.h_dt -= mj * dvdr * r_inv / rhoj * wi_dr;
@@ -268,4 +329,4 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_vec_force(
       "function does not exist yet!");
 }
 
-#endif /* SWIFT_RUNNER_IACT_MINIMAL_H */
+#endif /* SWIFT_MINIMAL_HYDRO_IACT_H */

src/hydro/Minimal/hydro_io.h

@@ -16,7 +16,25 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  ******************************************************************************/
+#ifndef SWIFT_MINIMAL_HYDRO_IO_H
+#define SWIFT_MINIMAL_HYDRO_IO_H
 
+/**
+ * @file Minimal/hydro_io.h
+ * @brief Minimal conservative implementation of SPH (i/o routines)
+ *
+ * The thermal variable is the internal energy (u). Simple constant
+ * viscosity term without switches is implemented. No thermal conduction
+ * term is implemented.
+ *
+ * This corresponds to equations (43), (44), (45), (101), (103)  and (104) with
+ * \f$\beta=3\f$ and \f$\alpha_u=0\f$ of
+ * Price, D., Journal of Computational Physics, 2012, Volume 231, Issue 3,
+ * pp. 759-794.
+ */
+
+#include "adiabatic_index.h"
+#include "hydro.h"
 #include "io_properties.h"
 #include "kernel_hydro.h"
 
@@ -51,6 +69,16 @@ void hydro_read_particles(struct part* parts, struct io_props* list,
                                 UNIT_CONV_DENSITY, parts, rho);
 }
 
+float convert_S(struct engine* e, struct part* p) {
+
+  return hydro_get_entropy(p, 0);
+}
+
+float convert_P(struct engine* e, struct part* p) {
+
+  return hydro_get_pressure(p, 0);
+}
+
 /**
  * @brief Specifies which particle fields to write to a dataset
  *
@@ -61,7 +89,7 @@ void hydro_read_particles(struct part* parts, struct io_props* list,
 void hydro_write_particles(struct part* parts, struct io_props* list,
                            int* num_fields) {
 
-  *num_fields = 8;
+  *num_fields = 10;
 
   /* List what we want to write */
   list[0] = io_make_output_field("Coordinates", DOUBLE, 3, UNIT_CONV_LENGTH,
@@ -80,6 +108,11 @@ void hydro_write_particles(struct part* parts, struct io_props* list,
                                  UNIT_CONV_ACCELERATION, parts, a_hydro);
   list[7] =
       io_make_output_field("Density", FLOAT, 1, UNIT_CONV_DENSITY, parts, rho);
+  list[8] = io_make_output_field_convert_part("Entropy", FLOAT, 1,
+                                              UNIT_CONV_ENTROPY_PER_UNIT_MASS,
+                                              parts, rho, convert_S);
+  list[9] = io_make_output_field_convert_part(
+      "Pressure", FLOAT, 1, UNIT_CONV_PRESSURE, parts, rho, convert_P);
 }
 
 /**
@@ -90,8 +123,9 @@ void writeSPHflavour(hid_t h_grpsph) {
 
   /* Viscosity and thermal conduction */
   /* Nothing in this minimal model... */
-  writeAttribute_s(h_grpsph, "Thermal Conductivity Model", "No model");
-  writeAttribute_s(h_grpsph, "Viscosity Model", "No model");
+  writeAttribute_s(h_grpsph, "Thermal Conductivity Model", "No treatment");
+  writeAttribute_s(h_grpsph, "Viscosity Model",
+                   "Minimal treatment as in Monaghan (1992)");
 
   /* Time integration properties */
   writeAttribute_f(h_grpsph, "Maximal Delta u change over dt",
@@ -104,3 +138,5 @@ void writeSPHflavour(hid_t h_grpsph) {
  * @return 1 if entropy is in 'internal energy', 0 otherwise.
  */
 int writeEntropyFlag() { return 0; }
+
+#endif /* SWIFT_MINIMAL_HYDRO_IO_H */

src/hydro/Minimal/hydro_part.h

@@ -16,6 +16,22 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  ******************************************************************************/
+#ifndef SWIFT_MINIMAL_HYDRO_PART_H
+#define SWIFT_MINIMAL_HYDRO_PART_H
+
+/**
+ * @file Minimal/hydro_part.h
+ * @brief Minimal conservative implementation of SPH (Particle definition)
+ *
+ * The thermal variable is the internal energy (u). Simple constant
+ * viscosity term without switches is implemented. No thermal conduction
+ * term is implemented.
+ *
+ * This corresponds to equations (43), (44), (45), (101), (103)  and (104) with
+ * \f$\beta=3\f$ and \f$\alpha_u=0\f$ of
+ * Price, D., Journal of Computational Physics, 2012, Volume 231, Issue 3,
+ * pp. 759-794.
+ */
 
 /**
  * @brief Particle fields not needed during the SPH loops over neighbours.
@@ -31,8 +47,6 @@ struct xpart {
 
   float v_full[3]; /*!< Velocity at the last full step. */
 
-  float u_full; /*!< Thermal energy at the last full step. */
-
 } __attribute__((aligned(xpart_align)));
 
 /**
@@ -107,3 +121,5 @@ struct part {
   struct gpart* gpart; /*!< Pointer to corresponding gravity part. */
 
 } __attribute__((aligned(part_align)));
+
+#endif /* SWIFT_MINIMAL_HYDRO_PART_H */

src/hydro_properties.c

@@ -70,7 +70,7 @@ void hydro_props_print(const struct hydro_props *p) {
   message(
       "Hydrodynamic integration: Max change of volume: %.2f "
       "(max|dlog(h)/dt|=%f).",
-      powf(expf(p->log_max_h_change), hydro_dimension), p->log_max_h_change);
+      pow_dimension(expf(p->log_max_h_change)), p->log_max_h_change);
 
   if (p->max_smoothing_iterations != hydro_props_default_max_iterations)
     message("Maximal iterations in ghost task set to %d (default is %d)",
@@ -90,8 +90,8 @@ void hydro_props_print_snapshot(hid_t h_grpsph, const struct hydro_props *p) {
   writeAttribute_f(h_grpsph, "CFL parameter", p->CFL_condition);
   writeAttribute_f(h_grpsph, "Volume log(max(delta h))", p->log_max_h_change);
   writeAttribute_f(h_grpsph, "Volume max change time-step",
-                   powf(expf(p->log_max_h_change), 3.f));
-  writeAttribute_f(h_grpsph, "Max ghost iterations",
+                   pow_dimension(expf(p->log_max_h_change)));
+  writeAttribute_i(h_grpsph, "Max ghost iterations",
                    p->max_smoothing_iterations);
 }
 #endif