From 4efc01bccbfaf97e13519e61f0b6d4241fdc18bd Mon Sep 17 00:00:00 2001
From: Matthieu Schaller <matthieu.schaller@durham.ac.uk>
Date: Thu, 16 Mar 2017 09:34:03 +0800
Subject: [PATCH] Added pressure to entropy and pressure to internal energy
 functions to the equation of state definition.

---
 src/dimension.h         |  2 +-
 src/equation_of_state.h | 59 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/src/dimension.h b/src/dimension.h
index 9169a0796e..7c58b5b846 100644
--- a/src/dimension.h
+++ b/src/dimension.h
@@ -229,7 +229,7 @@ __attribute__((always_inline)) INLINE static float get_radius_dimension_sphere(
 
   error("The dimension is not defined !");
   return 0.f;
-  
+
 #endif
 }
 
diff --git a/src/equation_of_state.h b/src/equation_of_state.h
index 5e570fc634..28c97c7b96 100644
--- a/src/equation_of_state.h
+++ b/src/equation_of_state.h
@@ -69,6 +69,21 @@ __attribute__((always_inline)) INLINE static float gas_pressure_from_entropy(
   return entropy * pow_gamma(density);
 }
 
+/**
+ * @brief Returns the entropy given density and pressure.
+ *
+ * Computes \f$A = \frac{P}{\rho^\gamma}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param pressure The pressure \f$P\f$.
+ * @return The entropy \f$A\f$.
+ */
+__attribute__((always_inline)) INLINE static float gas_entropy_from_pressure(
+    float density, float pressure) {
+
+  return pressure * pow_minus_gamma(density);
+}
+
 /**
  * @brief Returns the sound speed given density and entropy
  *
@@ -111,6 +126,20 @@ gas_pressure_from_internal_energy(float density, float u) {
   return hydro_gamma_minus_one * u * density;
 }
 
+/**
+ * @brief Returns the internal energy given density and pressure.
+ *
+ * Computes \f$u = \frac{1}{\gamma - 1}\frac{P}{\rho}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param pressure The pressure \f$P\f$.
+ * @return The internal energy \f$u\f$.
+ */
+__attribute__((always_inline)) INLINE static float
+gas_internal_energy_from_pressure(float density, float pressure) {
+  return hydro_one_over_gamma_minus_one * pressure / density;
+}
+
 /**
  * @brief Returns the sound speed given density and internal energy
  *
@@ -172,6 +201,22 @@ __attribute__((always_inline)) INLINE static float gas_pressure_from_entropy(
   return hydro_gamma_minus_one * const_isothermal_internal_energy * density;
 }
 
+/**
+ * @brief Returns the entropy given density and pressure.
+ *
+ * Computes \f$A = \frac{P}{\rho^\gamma}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param pressure The pressure \f$P\f$ (ignored).
+ * @return The entropy \f$A\f$.
+ */
+__attribute__((always_inline)) INLINE static float gas_entropy_from_pressure(
+    float density, float pressure) {
+
+  return hydro_gamma_minus_one * const_isothermal_internal_energy *
+         pow_minus_gamma_minus_one(density);
+}
+
 /**
  * @brief Returns the sound speed given density and entropy
  *
@@ -219,6 +264,20 @@ gas_pressure_from_internal_energy(float density, float u) {
   return hydro_gamma_minus_one * const_isothermal_internal_energy * density;
 }
 
+/**
+ * @brief Returns the internal energy given density and pressure.
+ *
+ * Just returns the constant internal energy.
+ *
+ * @param density The density \f$\rho\f$ (ignored).
+ * @param pressure The pressure \f$P\f$ (ignored).
+ * @return The internal energy \f$u\f$ (which is constant).
+ */
+__attribute__((always_inline)) INLINE static float
+gas_internal_energy_from_pressure(float density, float pressure) {
+  return const_isothermal_energy;
+}
+
 /**
  * @brief Returns the sound speed given density and internal energy
  *
-- 
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