Add EOS temperature from entropy floor

This merge request fixes a difference we implemented differently in SWIFT as compared to EAGLE. Instead of calculating the EOS temperature from the star formation EOS we need to calculate this from the entropy floor, this merge request does that. I also have run the idealized disk without problems, it produces the same result. threshold density (numb/cm^3) is around 0.03 for solar, that still has a temperature above the threshold given by around (0.03/0.1)^(1/3)8000 K10^.5 = 17000 K, so in the case of my disk, it produces exactly the same result as before. Any comments on the code?

src/entropy_floor/EAGLE/entropy_floor.h

@@ -137,9 +137,68 @@ static INLINE float entropy_floor(
 }
 
 /**
+ * @brief Compute the temperature from the entropy floor for a given #part
+ *
+ * Calculate the EoS temperature, the particle is not updated.
+ * This is the temperature exactly corresponding to the imposed EoS shape.
+ * It only matches the entropy returned by the entropy_floor() function
+ * for a neutral gas with primoridal abundance.
+ *
+ * @param p The #part.
+ * @param cosmo The cosmological model.
+ * @param props The properties of the entropy floor.
+ */
+static INLINE float entropy_floor_temperature(
+    const struct part *p, const struct cosmology *cosmo,
+    const struct entropy_floor_properties *props) {
+
+  /* Physical density in internal units */
+  const float rho = hydro_get_physical_density(p, cosmo);
+
+  /* Critical density at this redshift.
+   * Recall that this is 0 in a non-cosmological run */
+  const float rho_crit = cosmo->critical_density;
+  const float rho_crit_baryon = cosmo->Omega_b * rho_crit;
+
+  /* Physical */
+  float temperature = 0.f;
+
+  /* Are we in the regime of the Jeans equation of state? */
+  if ((rho >= rho_crit_baryon * props->Jeans_over_density_threshold) &&
+      (rho >= props->Jeans_density_threshold)) {
+
+    const float jeans_slope = props->Jeans_gamma_effective - 1.f;
+
+    const float temperature_Jeans =
+        props->Jeans_temperature_norm *
+        pow(rho * props->Jeans_density_threshold_inv, jeans_slope);
+
+    temperature = max(temperature, temperature_Jeans);
+  }
+
+  /* Are we in the regime of the Cool equation of state? */
+  if ((rho >= rho_crit_baryon * props->Cool_over_density_threshold) &&
+      (rho >= props->Cool_density_threshold)) {
+
+    const float cool_slope = props->Cool_gamma_effective - 1.f;
+
+    const float temperature_Cool =
+        props->Cool_temperature_norm *
+        pow(rho * props->Cool_density_threshold_inv, cool_slope);
+
+    temperature = max(temperature, temperature_Cool);
+  }
+
+  return temperature;
+}
+
+/**
  * @brief Initialise the entropy floor by reading the parameters and converting
  * to internal units.
  *
+ * The input temperatures and number densities are converted to entropy and
+ * density assuming a neutral gas of primoridal abundance.
+ *
  * @param params The YAML parameter file.
  * @param us The system of units used internally.
  * @param phys_const The physical constants.