Added a 'sound speed' variable to the Minimal SPH particle to save redundant calculations.

src/const.h

@@ -63,8 +63,8 @@
 //#define WENDLAND_C6_KERNEL
 
 /* SPH variant to use */
-//#define MINIMAL_SPH
-#define GADGET2_SPH
+#define MINIMAL_SPH
+//#define GADGET2_SPH
 //#define HOPKINS_PE_SPH
 //#define DEFAULT_SPH
 //#define GIZMO_SPH

src/hydro/Minimal/hydro.h

@@ -141,6 +141,12 @@ __attribute__((always_inline)) INLINE static void hydro_set_internal_energy(
 
   /* Compute the pressure */
   const float pressure = gas_pressure_from_internal_energy(p->rho, p->u);
+
+  /* Compute the sound speed from the pressure*/
+  const float rho_inv = 1.f / p->rho;
+  const float soundspeed = sqrtf(hydro_gamma * pressure * rho_inv);
+
+  p->force.soundspeed = soundspeed;
   p->force.pressure = pressure;
 }
 
@@ -160,6 +166,12 @@ __attribute__((always_inline)) INLINE static void hydro_set_entropy(
 
   /* Compute the pressure */
   const float pressure = gas_pressure_from_internal_energy(p->rho, p->u);
+
+  /* Compute the sound speed from the pressure*/
+  const float rho_inv = 1.f / p->rho;
+  const float soundspeed = sqrtf(hydro_gamma * pressure * rho_inv);
+
+  p->force.soundspeed = soundspeed;
   p->force.pressure = pressure;
 }
 
@@ -277,10 +289,15 @@ __attribute__((always_inline)) INLINE static void hydro_prepare_force(
     struct part *restrict p, struct xpart *restrict xp, int ti_current,
     double timeBase) {
 
+  /* Compute the pressure */
   const float half_dt = (ti_current - (p->ti_begin + p->ti_end) / 2) * timeBase;
   const float pressure = hydro_get_pressure(p, half_dt);
+
   const float rho_inv = 1.f / p->rho;
 
+  /* Compute the sound speed */
+  const float soundspeed = sqrtf(hydro_gamma * pressure * rho_inv);
+
   /* Compute the "grad h" term */
   const float grad_h_term =
       1.f / (1.f + hydro_dimension_inv * p->h * p->density.rho_dh * rho_inv);
@@ -288,6 +305,7 @@ __attribute__((always_inline)) INLINE static void hydro_prepare_force(
   /* Update variables. */
   p->force.f = grad_h_term;
   p->force.pressure = pressure;
+  p->force.soundspeed = soundspeed;
 }
 
 /**
@@ -347,7 +365,15 @@ __attribute__((always_inline)) INLINE static void hydro_predict_extra(
 
   /* 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);
+  const float pressure = hydro_get_pressure(p, dt_entr);
+
+  const float rho_inv = 1.f / p->rho;
+
+  /* Compute the new sound speed */
+  const float soundspeed = sqrtf(hydro_gamma * pressure * rho_inv);
+
+  p->force.pressure = pressure;
+  p->force.soundspeed = soundspeed;
 }
 
 /**
@@ -392,6 +418,12 @@ __attribute__((always_inline)) INLINE static void hydro_kick_extra(
 
   /* Compute the pressure */
   const float pressure = gas_pressure_from_internal_energy(p->rho, p->u);
+
+  /* Compute the sound speed from the pressure*/
+  const float rho_inv = 1.f / p->rho;
+  const float soundspeed = sqrtf(hydro_gamma * pressure * rho_inv);
+
+  p->force.soundspeed = soundspeed;
   p->force.pressure = pressure;
 }
 

src/hydro/Minimal/hydro_iact.h

@@ -165,8 +165,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_force(
   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 ci = pi->force.soundspeed;
+  const float cj = pj->force.soundspeed;
   const float v_sig = ci + cj - 3.f * mu_ij;
 
   /* Construct the full viscosity term */
@@ -276,8 +276,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
   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 ci = pi->force.soundspeed;
+  const float cj = pj->force.soundspeed;
   const float v_sig = ci + cj - 3.f * mu_ij;
 
   /* Construct the full viscosity term */

src/hydro/Minimal/hydro_part.h

@@ -131,6 +131,9 @@ struct part {
       /*! Particle pressure. */
       float pressure;
 
+      /*! Particle soundspeed. */
+      float soundspeed;
+
       /*! Particle signal velocity */
       float v_sig;