Also update the EAGLE stars model with the new compulsory particle fields and function signatures.

src/runner.c

@@ -209,7 +209,8 @@ void runner_do_stars_ghost(struct runner *r, struct cell *c, int timer) {
           /* Skip if h is already h_max and we don't have enough neighbours */
           if ((sp->h >= stars_h_max) && (f < 0.f)) {
 
-            stars_reset_acceleration(sp);
+            stars_reset_feedback(sp);
+
             /* Ok, we are done with this particle */
             continue;
           }
@@ -260,7 +261,7 @@ void runner_do_stars_ghost(struct runner *r, struct cell *c, int timer) {
         }
 
         /* We now have a particle whose smoothing length has converged */
-        stars_reset_acceleration(sp);
+        stars_reset_feedback(sp);
 
         /* Compute the stellar evolution  */
         stars_evolve_spart(sp, stars_properties, cosmo);

src/stars/Default/stars.h

@@ -100,6 +100,7 @@ __attribute__((always_inline)) INLINE static void stars_reset_predicted_values(
  */
 __attribute__((always_inline)) INLINE static void stars_end_feedback(
     struct spart* sp) {
+
   sp->feedback.h_dt *= sp->h * hydro_dimension_inv;
 }
 
@@ -174,7 +175,7 @@ __attribute__((always_inline)) INLINE static void stars_evolve_spart(
  *
  * @param p The particle to act upon
  */
-__attribute__((always_inline)) INLINE static void stars_reset_acceleration(
+__attribute__((always_inline)) INLINE static void stars_reset_feedback(
     struct spart* restrict p) {
 
   /* Reset time derivative */
@@ -186,4 +187,5 @@ __attribute__((always_inline)) INLINE static void stars_reset_acceleration(
   p->num_ngb_force = 0;
 #endif
 }
+
 #endif /* SWIFT_DEFAULT_STARS_H */

src/stars/Default/stars_part.h

@@ -61,6 +61,7 @@ struct spart {
   timebin_t time_bin;
 
   struct {
+
     /* Number of neighbours. */
     float wcount;
 
@@ -69,18 +70,19 @@ struct spart {
 
   } density;
 
-  /*! Tracer structure */
-  struct tracers_xpart_data tracers_data;
-
-  /*! Chemistry structure */
-  struct chemistry_part_data chemistry_data;
-
   struct {
+
     /* Change in smoothing length over time. */
     float h_dt;
 
   } feedback;
 
+  /*! Tracer structure */
+  struct tracers_xpart_data tracers_data;
+
+  /*! Chemistry structure */
+  struct chemistry_part_data chemistry_data;
+
 #ifdef SWIFT_DEBUG_CHECKS
 
   /* Time of the last drift */

src/stars/EAGLE/stars.h

@@ -66,6 +66,25 @@ __attribute__((always_inline)) INLINE static void stars_init_spart(
   sp->density.wcount_dh = 0.f;
 }
 
+/**
+ * @brief Predict additional particle fields forward in time when drifting
+ *
+ * @param p The particle
+ * @param dt_drift The drift time-step for positions.
+ */
+__attribute__((always_inline)) INLINE static void stars_predict_extra(
+    struct spart* restrict sp, float dt_drift) {
+
+  const float h_inv = 1.f / sp->h;
+
+  /* Predict smoothing length */
+  const float w1 = sp->feedback.h_dt * h_inv * dt_drift;
+  if (fabsf(w1) < 0.2f)
+    sp->h *= approx_expf(w1); /* 4th order expansion of exp(w) */
+  else
+    sp->h *= expf(w1);
+}
+
 /**
  * @brief Sets the values to be predicted in the drifts to their values at a
  * kick time
@@ -82,8 +101,11 @@ __attribute__((always_inline)) INLINE static void stars_reset_predicted_values(
  *
  * @param sp The particle to act upon
  */
-__attribute__((always_inline)) INLINE static void stars_end_force(
-    struct spart* sp) {}
+__attribute__((always_inline)) INLINE static void stars_end_feedback(
+    struct spart* sp) {
+
+  sp->feedback.h_dt *= sp->h * hydro_dimension_inv;
+}
 
 /**
  * @brief Kick the additional variables
@@ -148,4 +170,25 @@ __attribute__((always_inline)) INLINE static void stars_evolve_spart(
     struct spart* restrict sp, const struct stars_props* stars_properties,
     const struct cosmology* cosmo) {}
 
+/**
+ * @brief Reset acceleration fields of a particle
+ *
+ * This is the equivalent of hydro_reset_acceleration.
+ * We do not compute the acceleration on star, therefore no need to use it.
+ *
+ * @param p The particle to act upon
+ */
+__attribute__((always_inline)) INLINE static void stars_reset_feedback(
+    struct spart* restrict p) {
+
+  /* Reset time derivative */
+  p->feedback.h_dt = 0.f;
+
+#ifdef DEBUG_INTERACTIONS_STARS
+  for (int i = 0; i < MAX_NUM_OF_NEIGHBOURS_STARS; ++i)
+    p->ids_ngbs_force[i] = -1;
+  p->num_ngb_force = 0;
+#endif
+}
+
 #endif /* SWIFT_EAGLE_STARS_H */

src/stars/EAGLE/stars_part.h

@@ -65,6 +65,7 @@ struct spart {
   timebin_t time_bin;
 
   struct {
+
     /* Number of neighbours. */
     float wcount;
 
@@ -73,8 +74,16 @@ struct spart {
 
   } density;
 
+  struct {
+
+    /* Change in smoothing length over time. */
+    float h_dt;
+
+  } feedback;
+
   /*! Union for the birth time and birht scale factor */
   union {
+
     /*! Birth time */
     float birth_time;