diff --git a/src/equation_of_state.c b/src/equation_of_state.c
index a792bc58cf13fa5f710dc1cd80713ff90e700b18..67557d604ae74d24a19b8049cfdf86bd5cc238ad 100644
--- a/src/equation_of_state.c
+++ b/src/equation_of_state.c
@@ -20,48 +20,7 @@
/* This object's header. */
#include "equation_of_state.h"
-/* local headers */
-#include "common_io.h"
-
/* Equation of state for the physics model
* (temporary ugly solution as a global variable) */
struct eos_parameters eos;
-void eos_init(struct eos_parameters *e, const struct swift_params *params) {
-
-#if defined(EOS_IDEAL_GAS)
-/* nothing to do here */
-#elif defined(EOS_ISOTHERMAL_GAS)
- e->isothermal_internal_energy =
- parser_get_param_float(params, "EoS:isothermal_internal_energy");
-#endif
-}
-
-void eos_print(const struct eos_parameters *e) {
-
-#if defined(EOS_IDEAL_GAS)
- message("Equation of state: Ideal gas.");
-#elif defined(EOS_ISOTHERMAL_GAS)
- message(
- "Equation of state: Isothermal with internal energy "
- "per unit mass set to %f.",
- e->isothermal_internal_energy);
-#endif
-
- message("Adiabatic index gamma: %f.", hydro_gamma);
-}
-
-#if defined(HAVE_HDF5)
-void eos_print_snapshot(hid_t h_grpsph, const struct eos_parameters *e) {
-
- io_write_attribute_f(h_grpsph, "Adiabatic index", hydro_gamma);
-
-#if defined(EOS_IDEAL_GAS)
- io_write_attribute_s(h_grpsph, "Equation of state", "Ideal gas");
-#elif defined(EOS_ISOTHERMAL_GAS)
- io_write_attribute_s(h_grpsph, "Equation of state", "Isothermal gas");
- io_write_attribute_f(h_grpsph, "Thermal energy per unit mass",
- e->isothermal_internal_energy);
-#endif
-}
-#endif
diff --git a/src/equation_of_state.h b/src/equation_of_state.h
index 76b8bb922133c9c4f29453a14068fe3f9044d66f..c678a90e3ffa5e29d964b00303cadbb8554778df 100644
--- a/src/equation_of_state.h
+++ b/src/equation_of_state.h
@@ -19,325 +19,16 @@
#ifndef SWIFT_EQUATION_OF_STATE_H
#define SWIFT_EQUATION_OF_STATE_H
-/**
- * @file equation_of_state.h
- * @brief Defines the equation of state of the gas we simulate in the form of
- * relations between thermodynamic quantities. These are later used internally
- * by all hydro schemes
- */
-
/* Config parameters. */
#include "../config.h"
-/* Some standard headers. */
-#include <math.h>
-
-/* Local headers. */
-#include "adiabatic_index.h"
-#include "debug.h"
-#include "inline.h"
-
-extern struct eos_parameters eos;
-
-/* ------------------------------------------------------------------------- */
+/* Import the right functions */
#if defined(EOS_IDEAL_GAS)
-
-struct eos_parameters {};
-
-/**
- * @brief Returns the internal energy given density and entropy
- *
- * Computes \f$u = \frac{S\rho^{\gamma-1} }{\gamma - 1}\f$.
- *
- * @param density The density \f$\rho\f$.
- * @param entropy The entropy \f$S\f$.
- */
-__attribute__((always_inline)) INLINE static float
-gas_internal_energy_from_entropy(float density, float entropy) {
-
- return entropy * pow_gamma_minus_one(density) *
- hydro_one_over_gamma_minus_one;
-}
-
-/**
- * @brief Returns the pressure given density and entropy
- *
- * Computes \f$P = S\rho^\gamma\f$.
- *
- * @param density The density \f$\rho\f$.
- * @param entropy The entropy \f$S\f$.
- */
-__attribute__((always_inline)) INLINE static float gas_pressure_from_entropy(
- float density, float 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
- *
- * Computes \f$c = \sqrt{\gamma S \rho^{\gamma-1}}\f$.
- *
- * @param density The density \f$\rho\f$.
- * @param entropy The entropy \f$S\f$.
- */
-__attribute__((always_inline)) INLINE static float gas_soundspeed_from_entropy(
- float density, float entropy) {
-
- return sqrtf(hydro_gamma * pow_gamma_minus_one(density) * entropy);
-}
-
-/**
- * @brief Returns the entropy given density and internal energy
- *
- * Computes \f$S = \frac{(\gamma - 1)u}{\rho^{\gamma-1}}\f$.
- *
- * @param density The density \f$\rho\f$
- * @param u The internal energy \f$u\f$
- */
-__attribute__((always_inline)) INLINE static float
-gas_entropy_from_internal_energy(float density, float u) {
-
- return hydro_gamma_minus_one * u * pow_minus_gamma_minus_one(density);
-}
-
-/**
- * @brief Returns the pressure given density and internal energy
- *
- * Computes \f$P = (\gamma - 1)u\rho\f$.
- *
- * @param density The density \f$\rho\f$
- * @param u The internal energy \f$u\f$
- */
-__attribute__((always_inline)) INLINE static float
-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
- *
- * Computes \f$c = \sqrt{\gamma (\gamma - 1) u }\f$.
- *
- * @param density The density \f$\rho\f$
- * @param u The internal energy \f$u\f$
- */
-__attribute__((always_inline)) INLINE static float
-gas_soundspeed_from_internal_energy(float density, float u) {
-
- return sqrtf(u * hydro_gamma * hydro_gamma_minus_one);
-}
-
-/**
- * @brief Returns the sound speed given density and pressure
- *
- * Computes \f$c = \sqrt{\frac{\gamma P}{\rho} }\f$.
- *
- * @param density The density \f$\rho\f$
- * @param P The pressure \f$P\f$
- */
-__attribute__((always_inline)) INLINE static float gas_soundspeed_from_pressure(
- float density, float P) {
-
- const float density_inv = 1.f / density;
- return sqrtf(hydro_gamma * P * density_inv);
-}
-
-/* ------------------------------------------------------------------------- */
+#include "./equation_of_state/ideal_gas/equation_of_state.h"
#elif defined(EOS_ISOTHERMAL_GAS)
-
-struct eos_parameters {
-
- /*! Thermal energy per unit mass */
- float isothermal_internal_energy;
-};
-
-/**
- * @brief Returns the internal energy given density and entropy
- *
- * Since we are using an isothermal EoS, the entropy and density values are
- * ignored.
- * Computes \f$u = u_{cst}\f$.
- *
- * @param density The density \f$\rho\f$.
- * @param entropy The entropy \f$S\f$.
- */
-__attribute__((always_inline)) INLINE static float
-gas_internal_energy_from_entropy(float density, float entropy) {
-
- return eos.isothermal_internal_energy;
-}
-
-/**
- * @brief Returns the pressure given density and entropy
- *
- * Since we are using an isothermal EoS, the entropy value is ignored.
- * Computes \f$P = (\gamma - 1)u_{cst}\rho\f$.
- *
- * @param density The density \f$\rho\f$.
- * @param entropy The entropy \f$S\f$.
- */
-__attribute__((always_inline)) INLINE static float gas_pressure_from_entropy(
- float density, float entropy) {
-
- return hydro_gamma_minus_one * eos.isothermal_internal_energy * density;
-}
-
-/**
- * @brief Returns the entropy given density and pressure.
- *
- * Since we are using an isothermal EoS, the pressure value is ignored.
- * Computes \f$A = (\gamma - 1)u_{cst}\rho^{-(\gamma-1)}\f$.
- *
- * @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 * eos.isothermal_internal_energy *
- pow_minus_gamma_minus_one(density);
-}
-
-/**
- * @brief Returns the sound speed given density and entropy
- *
- * Since we are using an isothermal EoS, the entropy and density values are
- * ignored.
- * Computes \f$c = \sqrt{u_{cst} \gamma (\gamma-1)}\f$.
- *
- * @param density The density \f$\rho\f$.
- * @param entropy The entropy \f$S\f$.
- */
-__attribute__((always_inline)) INLINE static float gas_soundspeed_from_entropy(
- float density, float entropy) {
-
- return sqrtf(eos.isothermal_internal_energy * hydro_gamma *
- hydro_gamma_minus_one);
-}
-
-/**
- * @brief Returns the entropy given density and internal energy
- *
- * Since we are using an isothermal EoS, the energy value is ignored.
- * Computes \f$S = \frac{(\gamma - 1)u_{cst}}{\rho^{\gamma-1}}\f$.
- *
- * @param density The density \f$\rho\f$
- * @param u The internal energy \f$u\f$
- */
-__attribute__((always_inline)) INLINE static float
-gas_entropy_from_internal_energy(float density, float u) {
-
- return hydro_gamma_minus_one * eos.isothermal_internal_energy *
- pow_minus_gamma_minus_one(density);
-}
-
-/**
- * @brief Returns the pressure given density and internal energy
- *
- * Since we are using an isothermal EoS, the energy value is ignored.
- * Computes \f$P = (\gamma - 1)u_{cst}\rho\f$.
- *
- * @param density The density \f$\rho\f$
- * @param u The internal energy \f$u\f$
- */
-__attribute__((always_inline)) INLINE static float
-gas_pressure_from_internal_energy(float density, float u) {
-
- return hydro_gamma_minus_one * eos.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 eos.isothermal_internal_energy;
-}
-
-/**
- * @brief Returns the sound speed given density and internal energy
- *
- * Since we are using an isothermal EoS, the energy and density values are
- * ignored.
- * Computes \f$c = \sqrt{u_{cst} \gamma (\gamma-1)}\f$.
- *
- * @param density The density \f$\rho\f$
- * @param u The internal energy \f$u\f$
- */
-__attribute__((always_inline)) INLINE static float
-gas_soundspeed_from_internal_energy(float density, float u) {
-
- return sqrtf(eos.isothermal_internal_energy * hydro_gamma *
- hydro_gamma_minus_one);
-}
-
-/**
- * @brief Returns the sound speed given density and pressure
- *
- * Since we are using an isothermal EoS, the pressure and density values are
- * ignored.
- * Computes \f$c = \sqrt{u_{cst} \gamma (\gamma-1)}\f$.
- *
- * @param density The density \f$\rho\f$
- * @param P The pressure \f$P\f$
- */
-__attribute__((always_inline)) INLINE static float gas_soundspeed_from_pressure(
- float density, float P) {
-
- return sqrtf(eos.isothermal_internal_energy * hydro_gamma *
- hydro_gamma_minus_one);
-}
-
-/* ------------------------------------------------------------------------- */
+#include "./equation_of_state/isothermal/equation_of_state.h"
#else
-
-#error "An Equation of state needs to be chosen in const.h !"
-
-#endif
-
-void eos_init(struct eos_parameters *e, const struct swift_params *params);
-void eos_print(const struct eos_parameters *e);
-
-#if defined(HAVE_HDF5)
-void eos_print_snapshot(hid_t h_grpsph, const struct eos_parameters *e);
+#error "Invalid choice of equation of state"
#endif
#endif /* SWIFT_EQUATION_OF_STATE_H */
diff --git a/src/equation_of_state/ideal_gas/equation_of_state.h b/src/equation_of_state/ideal_gas/equation_of_state.h
new file mode 100644
index 0000000000000000000000000000000000000000..e668f65580c50191cf53dac567e60019b11b7066
--- /dev/null
+++ b/src/equation_of_state/ideal_gas/equation_of_state.h
@@ -0,0 +1,218 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_IDEAL_GAS_EQUATION_OF_STATE_H
+#define SWIFT_IDEAL_GAS_EQUATION_OF_STATE_H
+
+/**
+ * @file equation_of_state.h
+ * @brief Defines the equation of state of the gas we simulate in the form of
+ * relations between thermodynamic quantities. These are later used internally
+ * by all hydro schemes
+ */
+
+/* Config parameters. */
+#include "../config.h"
+
+/* Some standard headers. */
+#include <math.h>
+
+/* Local headers. */
+#include "adiabatic_index.h"
+#include "common_io.h"
+#include "debug.h"
+#include "inline.h"
+
+extern struct eos_parameters eos;
+/* ------------------------------------------------------------------------- */
+
+struct eos_parameters {};
+
+/**
+ * @brief Returns the internal energy given density and entropy
+ *
+ * Computes \f$u = \frac{S\rho^{\gamma-1} }{\gamma - 1}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param entropy The entropy \f$S\f$.
+ */
+__attribute__((always_inline)) INLINE static float
+gas_internal_energy_from_entropy(float density, float entropy) {
+
+ return entropy * pow_gamma_minus_one(density) *
+ hydro_one_over_gamma_minus_one;
+}
+
+/**
+ * @brief Returns the pressure given density and entropy
+ *
+ * Computes \f$P = S\rho^\gamma\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param entropy The entropy \f$S\f$.
+ */
+__attribute__((always_inline)) INLINE static float gas_pressure_from_entropy(
+ float density, float 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
+ *
+ * Computes \f$c = \sqrt{\gamma S \rho^{\gamma-1}}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param entropy The entropy \f$S\f$.
+ */
+__attribute__((always_inline)) INLINE static float gas_soundspeed_from_entropy(
+ float density, float entropy) {
+
+ return sqrtf(hydro_gamma * pow_gamma_minus_one(density) * entropy);
+}
+
+/**
+ * @brief Returns the entropy given density and internal energy
+ *
+ * Computes \f$S = \frac{(\gamma - 1)u}{\rho^{\gamma-1}}\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param u The internal energy \f$u\f$
+ */
+__attribute__((always_inline)) INLINE static float
+gas_entropy_from_internal_energy(
+ float density, float u) {
+
+ return hydro_gamma_minus_one * u * pow_minus_gamma_minus_one(density);
+}
+
+/**
+ * @brief Returns the pressure given density and internal energy
+ *
+ * Computes \f$P = (\gamma - 1)u\rho\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param u The internal energy \f$u\f$
+ */
+__attribute__((always_inline)) INLINE static float
+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
+ *
+ * Computes \f$c = \sqrt{\gamma (\gamma - 1) u }\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param u The internal energy \f$u\f$
+ */
+__attribute__((always_inline)) INLINE static float
+gas_soundspeed_from_internal_energy(
+ float density, float u) {
+
+ return sqrtf(u * hydro_gamma * hydro_gamma_minus_one);
+}
+
+/**
+ * @brief Returns the sound speed given density and pressure
+ *
+ * Computes \f$c = \sqrt{\frac{\gamma P}{\rho} }\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param P The pressure \f$P\f$
+ */
+__attribute__((always_inline)) INLINE static float gas_soundspeed_from_pressure(
+ float density, float P) {
+
+ const float density_inv = 1.f / density;
+ return sqrtf(hydro_gamma * P * density_inv);
+}
+
+/**
+ * @brief Initialize the eos parameters
+ *
+ * @param e The #eos_paramters
+ * @param params The parsed parameters
+ */
+__attribute__((always_inline)) INLINE static void eos_init(
+ struct eos_parameters *e, const struct swift_params *params) {}
+
+/**
+ * @brief Print the equation of state
+ *
+ * @param e The #eos_parameters
+ */
+__attribute__((always_inline)) INLINE static void eos_print(
+ const struct eos_parameters *e) {
+
+ message("Equation of state: Ideal gas.");
+
+ message("Adiabatic index gamma: %f.", hydro_gamma);
+}
+
+
+#if defined(HAVE_HDF5)
+/**
+ * @brief Write equation of state information to the snapshot
+ *
+ * @param h_grpsph The HDF5 group in which to write
+ * @param e The #eos_parameters
+ */
+__attribute__((always_inline)) INLINE static void eos_print_snapshot(
+ hid_t h_grpsph, const struct eos_parameters *e ) {
+
+ io_write_attribute_f(h_grpsph, "Adiabatic index", hydro_gamma);
+
+ io_write_attribute_s(h_grpsph, "Equation of state", "Ideal gas");
+}
+#endif
+
+#endif /* SWIFT_IDEAL_GAS_EQUATION_OF_STATE_H */
diff --git a/src/equation_of_state/isothermal/equation_of_state.h b/src/equation_of_state/isothermal/equation_of_state.h
new file mode 100644
index 0000000000000000000000000000000000000000..ccd1450e3e5b29d53d787762114343f633050753
--- /dev/null
+++ b/src/equation_of_state/isothermal/equation_of_state.h
@@ -0,0 +1,247 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_ISOTHERMAL_EQUATION_OF_STATE_H
+#define SWIFT_ISOTHERMAL_EQUATION_OF_STATE_H
+
+/**
+ * @file equation_of_state.h
+ * @brief Defines the equation of state of the gas we simulate in the form of
+ * relations between thermodynamic quantities. These are later used internally
+ * by all hydro schemes
+ */
+
+/* Config parameters. */
+#include "../config.h"
+
+/* Some standard headers. */
+#include <math.h>
+
+/* Local headers. */
+#include "adiabatic_index.h"
+#include "common_io.h"
+#include "debug.h"
+#include "inline.h"
+
+extern struct eos_parameters eos;
+/* ------------------------------------------------------------------------- */
+
+struct eos_parameters {
+
+ /*! Thermal energy per unit mass */
+ float isothermal_internal_energy;
+};
+
+/**
+ * @brief Returns the internal energy given density and entropy
+ *
+ * Since we are using an isothermal EoS, the entropy and density values are
+ * ignored.
+ * Computes \f$u = u_{cst}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param entropy The entropy \f$S\f$.
+ */
+__attribute__((always_inline)) INLINE static float
+gas_internal_energy_from_entropy(float density, float entropy) {
+
+ return eos.isothermal_internal_energy;
+}
+
+/**
+ * @brief Returns the pressure given density and entropy
+ *
+ * Since we are using an isothermal EoS, the entropy value is ignored.
+ * Computes \f$P = (\gamma - 1)u_{cst}\rho\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param entropy The entropy \f$S\f$.
+ */
+__attribute__((always_inline)) INLINE static float gas_pressure_from_entropy(
+ float density, float entropy) {
+
+ return hydro_gamma_minus_one * eos.isothermal_internal_energy * density;
+}
+
+/**
+ * @brief Returns the entropy given density and pressure.
+ *
+ * Since we are using an isothermal EoS, the pressure value is ignored.
+ * Computes \f$A = (\gamma - 1)u_{cst}\rho^{-(\gamma-1)}\f$.
+ *
+ * @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 * eos.isothermal_internal_energy *
+ pow_minus_gamma_minus_one(density);
+}
+
+/**
+ * @brief Returns the sound speed given density and entropy
+ *
+ * Since we are using an isothermal EoS, the entropy and density values are
+ * ignored.
+ * Computes \f$c = \sqrt{u_{cst} \gamma (\gamma-1)}\f$.
+ *
+ * @param density The density \f$\rho\f$.
+ * @param entropy The entropy \f$S\f$.
+ */
+__attribute__((always_inline)) INLINE static float gas_soundspeed_from_entropy(
+ float density, float entropy) {
+
+ return sqrtf(eos.isothermal_internal_energy * hydro_gamma *
+ hydro_gamma_minus_one);
+}
+
+/**
+ * @brief Returns the entropy given density and internal energy
+ *
+ * Since we are using an isothermal EoS, the energy value is ignored.
+ * Computes \f$S = \frac{(\gamma - 1)u_{cst}}{\rho^{\gamma-1}}\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param u The internal energy \f$u\f$
+ */
+__attribute__((always_inline)) INLINE static float
+gas_entropy_from_internal_energy(
+ float density, float u) {
+
+ return hydro_gamma_minus_one * eos.isothermal_internal_energy *
+ pow_minus_gamma_minus_one(density);
+}
+
+/**
+ * @brief Returns the pressure given density and internal energy
+ *
+ * Since we are using an isothermal EoS, the energy value is ignored.
+ * Computes \f$P = (\gamma - 1)u_{cst}\rho\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param u The internal energy \f$u\f$
+ */
+__attribute__((always_inline)) INLINE static float
+gas_pressure_from_internal_energy(
+ float density, float u) {
+
+ return hydro_gamma_minus_one * eos.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 eos.isothermal_internal_energy;
+}
+
+/**
+ * @brief Returns the sound speed given density and internal energy
+ *
+ * Since we are using an isothermal EoS, the energy and density values are
+ * ignored.
+ * Computes \f$c = \sqrt{u_{cst} \gamma (\gamma-1)}\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param u The internal energy \f$u\f$
+ */
+__attribute__((always_inline)) INLINE static float
+gas_soundspeed_from_internal_energy(
+ float density, float u) {
+
+ return sqrtf(eos.isothermal_internal_energy * hydro_gamma *
+ hydro_gamma_minus_one);
+}
+
+/**
+ * @brief Returns the sound speed given density and pressure
+ *
+ * Since we are using an isothermal EoS, the pressure and density values are
+ * ignored.
+ * Computes \f$c = \sqrt{u_{cst} \gamma (\gamma-1)}\f$.
+ *
+ * @param density The density \f$\rho\f$
+ * @param P The pressure \f$P\f$
+ */
+__attribute__((always_inline)) INLINE static float gas_soundspeed_from_pressure(
+ float density, float P) {
+
+ return sqrtf(eos.isothermal_internal_energy * hydro_gamma *
+ hydro_gamma_minus_one);
+}
+
+/* ------------------------------------------------------------------------- */
+
+/**
+ * @brief Initialize the eos parameters
+ *
+ * @param e The #eos_paramters
+ * @param params The parsed parameters
+ */
+__attribute__((always_inline)) INLINE static void eos_init(
+ struct eos_parameters *e, const struct swift_params *params) {
+
+ e->isothermal_internal_energy =
+ parser_get_param_float(params, "EoS:isothermal_internal_energy");
+}
+
+/**
+ * @brief Print the equation of state
+ *
+ * @param e The #eos_parameters
+ */
+__attribute__((always_inline)) INLINE static void eos_print(
+ const struct eos_parameters *e) {
+
+ message(
+ "Equation of state: Isothermal with internal energy "
+ "per unit mass set to %f.",
+ e->isothermal_internal_energy);
+
+ message("Adiabatic index gamma: %f.", hydro_gamma);
+}
+
+#if defined(HAVE_HDF5)
+/**
+ * @brief Write equation of state information to the snapshot
+ *
+ * @param h_grpsph The HDF5 group in which to write
+ * @param e The #eos_parameters
+ */
+__attribute__((always_inline)) INLINE static void eos_print_snapshot(
+ hid_t h_grpsph, const struct eos_parameters *e) {
+
+ io_write_attribute_f(h_grpsph, "Adiabatic index", hydro_gamma);
+
+ io_write_attribute_s(h_grpsph, "Equation of state", "Isothermal gas");
+ io_write_attribute_f(h_grpsph, "Thermal energy per unit mass",
+ e->isothermal_internal_energy);
+}
+#endif
+
+#endif /* SWIFT_ISOTHERMAL_EQUATION_OF_STATE_H */