more ideal gas bikeshedding

feos-org · g-bauer · Oct 13, 2025 · Aug 18, 2025 · Aug 18, 2025 · Aug 18, 2025
commit 424b77863ca4d6a50ef779250ebe36976c2faa19
diff --git a/crates/feos-core/src/equation_of_state/ideal_gas.rs b/crates/feos-core/src/equation_of_state/ideal_gas.rs
@@ -2,42 +2,12 @@ use num_dual::DualNum;
 
 /// Ideal gas Helmholtz energy contribution that allows calculating derivatives
 /// with respect to model parameters.
-pub trait IdealGasAD<D>: Clone {
+pub trait IdealGas<D = f64> {
     /// Implementation of an ideal gas model in terms of the
     /// logarithm of the cubic thermal de Broglie wavelength
     /// in units ln(A³) for each component in the system.
-    fn ln_lambda3_ad<D2: DualNum<f64, Inner = D> + Copy>(&self, temperature: D2) -> D2;
-
-    /// Implementation of an ideal gas model in terms of the
-    /// logarithm of the cubic thermal de Broglie wavelength
-    /// in units ln(A³) for each component in the system.
-    fn ln_lambda3(&self, temperature: D) -> D;
-
-    /// The name of the ideal gas model.
-    fn ideal_gas_model(&self) -> &'static str;
-}
-
-/// Ideal gas Helmholtz energy contribution without automatic differentiation.
-pub trait IdealGas {
-    /// Implementation of an ideal gas model in terms of the
-    /// logarithm of the cubic thermal de Broglie wavelength
-    /// in units ln(A³) for each component in the system.
-    fn ln_lambda3<D: DualNum<f64> + Copy>(&self, temperature: D) -> D;
+    fn ln_lambda3<D2: DualNum<f64, Inner = D> + Copy>(&self, temperature: D2) -> D2;
 
     /// The name of the ideal gas model.
     fn ideal_gas_model(&self) -> &'static str;
 }
-
-impl<T: IdealGas, D: DualNum<f64> + Copy> IdealGasAD<D> for &T {
-    fn ln_lambda3_ad<D2: DualNum<f64> + Copy>(&self, temperature: D2) -> D2 {
-        IdealGas::ln_lambda3(*self, temperature)
-    }
-
-    fn ln_lambda3(&self, temperature: D) -> D {
-        IdealGas::ln_lambda3(*self, temperature)
-    }
-
-    fn ideal_gas_model(&self) -> &'static str {
-        T::ideal_gas_model(self)
-    }
-}
diff --git a/crates/feos-core/src/equation_of_state/mod.rs b/crates/feos-core/src/equation_of_state/mod.rs
@@ -10,7 +10,7 @@ use quantity::{Energy, MolarEnergy, MolarWeight, Moles, Temperature, Volume};
 mod ideal_gas;
 mod residual;
 
-pub use ideal_gas::{IdealGas, IdealGasAD};
+pub use ideal_gas::IdealGas;
 pub use residual::{Molarweight, NoResidual, Residual, ResidualConst, ResidualDyn, Subset};
 
 /// An equation of state consisting of an ideal gas model
@@ -112,19 +112,17 @@ pub trait Total<N: Dim = Dyn, D: DualNum<f64> + Copy = f64>: Residual<N, D>
 where
     DefaultAllocator: Allocator<N>,
 {
-    type IdealGas<'a>: IdealGasAD<D>
-    where
-        Self: 'a;
+    type IdealGas: IdealGas<D>;
 
     fn ideal_gas_model(&self) -> &'static str;
 
-    fn ideal_gas<'a>(&'a self) -> impl Iterator<Item = Self::IdealGas<'a>>;
+    fn ideal_gas(&self) -> impl Iterator<Item = &Self::IdealGas>;
 
     fn ln_lambda3<D2: DualNum<f64, Inner = D> + Copy>(&self, temperature: D2) -> OVector<D2, N> {
         OVector::from_iterator_generic(
             N::from_usize(self.components()),
             U1,
-            self.ideal_gas().map(|i| i.ln_lambda3_ad(temperature)),
+            self.ideal_gas().map(|i| i.ln_lambda3(temperature)),
         )
     }
 
@@ -142,12 +140,12 @@ where
             } else {
                 r.ln() - 1.0
             };
-            res += r * (i.ln_lambda3_ad(temperature) + ln_rho_m1)
+            res += r * (i.ln_lambda3(temperature) + ln_rho_m1)
         }
         res * molar_volume * temperature
     }
 
-    fn ideal_gas_helmholtz_energy_unit<D2: DualNum<f64, Inner = D> + Copy>(
+    fn ideal_gas_helmholtz_energy<D2: DualNum<f64, Inner = D> + Copy>(
         &self,
         temperature: Temperature<D2>,
         volume: Volume<D2>,
@@ -162,78 +160,40 @@ where
             &molefracs,
         )) * total_moles
     }
-
-    fn ideal_gas_molar_helmholtz_energy_0(
-        &self,
-        temperature: D,
-        molar_volume: D,
-        molefracs: &OVector<D, N>,
-    ) -> D {
-        let partial_density = molefracs / molar_volume;
-        let mut res = D::from(0.0);
-        for (i, &r) in self.ideal_gas().zip(partial_density.iter()) {
-            let ln_rho_m1 = if r.re() == 0.0 {
-                D::from(0.0)
-            } else {
-                r.ln() - 1.0
-            };
-            res += r * (i.ln_lambda3(temperature) + ln_rho_m1)
-        }
-        res * molar_volume * temperature
-    }
-
-    fn ideal_gas_helmholtz_energy_0(
-        &self,
-        temperature: Temperature<D>,
-        volume: Volume<D>,
-        moles: &Moles<OVector<D, N>>,
-    ) -> Energy<D> {
-        let total_moles = moles.sum();
-        let molefracs = moles / total_moles;
-        let molar_volume = volume / total_moles;
-        MolarEnergy::from_reduced(self.ideal_gas_molar_helmholtz_energy_0(
-            temperature.into_reduced(),
-            molar_volume.into_reduced(),
-            &molefracs,
-        )) * total_moles
-    }
 }
 
 impl<
     I: IdealGas + Clone + 'static,
     C: Deref<Target = EquationOfState<Vec<I>, R>> + Clone,
     R: ResidualDyn + 'static,
-    D: DualNum<f64> + Copy,
-> Total<Dyn, D> for C
+> Total<Dyn, f64> for C
 {
-    type IdealGas<'a>
-        = &'a I
-    where
-        Self: 'a;
+    type IdealGas = I;
 
     fn ideal_gas_model(&self) -> &'static str {
         self.ideal_gas[0].ideal_gas_model()
     }
 
-    fn ideal_gas<'a>(&'a self) -> impl Iterator<Item = Self::IdealGas<'a>> {
+    fn ideal_gas(&self) -> impl Iterator<Item = &Self::IdealGas> {
         self.ideal_gas.iter()
     }
 }
 
-impl<I: IdealGasAD<D>, R: ResidualConst<N, D> + 'static, D: DualNum<f64> + Copy, const N: usize>
-    Total<Const<N>, D> for EquationOfState<[I; N], R>
+impl<
+    I: IdealGas<D> + Clone,
+    R: ResidualConst<N, D> + 'static,
+    D: DualNum<f64> + Copy,
+    const N: usize,
+> Total<Const<N>, D> for EquationOfState<[I; N], R>
 {
-    type IdealGas<'a>
-        = I
-    where
-        I: 'a;
+    type IdealGas = I;
 
     fn ideal_gas_model(&self) -> &'static str {
         self.ideal_gas[0].ideal_gas_model()
     }
 
-    fn ideal_gas<'a>(&'a self) -> impl Iterator<Item = Self::IdealGas<'a>> {
-        self.ideal_gas.clone().into_iter()
+    fn ideal_gas(&self) -> impl Iterator<Item = &Self::IdealGas> {
+        self.ideal_gas.iter()
     }
 }
 

diff --git a/crates/feos-core/src/lib.rs b/crates/feos-core/src/lib.rs
@@ -34,8 +34,8 @@ mod parameter_fit;
 mod phase_equilibria;
 mod state;
 pub use equation_of_state::{
-    EquationOfState, IdealGas, IdealGasAD, Molarweight, NoResidual, Residual, ResidualConst,
-    ResidualDyn, Subset, Total,
+    EquationOfState, IdealGas, Molarweight, NoResidual, Residual, ResidualConst, ResidualDyn,
+    Subset, Total,
 };
 pub use errors::{FeosError, FeosResult};
 pub use parameter_fit::{BinaryModel, ParametersAD, PureModel};

diff --git a/crates/feos-core/src/state/properties.rs b/crates/feos-core/src/state/properties.rs
@@ -20,7 +20,7 @@ where
         let ideal_gas = || {
             quantity::ad::gradient_copy(
                 partial2(
-                    |n, &t, &v| self.eos.ideal_gas_helmholtz_energy_unit(t, v, &n),
+                    |n, &t, &v| self.eos.ideal_gas_helmholtz_energy(t, v, &n),
                     &self.temperature,
                     &self.volume,
                 ),
@@ -37,7 +37,7 @@ where
         let ideal_gas = || {
             quantity::ad::partial_hessian_copy(
                 partial(
-                    |(n, t), &v| self.eos.ideal_gas_helmholtz_energy_unit(t, v, &n),
+                    |(n, t), &v| self.eos.ideal_gas_helmholtz_energy(t, v, &n),
                     &self.volume,
                 ),
                 (&self.moles, self.temperature),
@@ -80,7 +80,7 @@ where
         let ideal_gas = || {
             -quantity::ad::first_derivative(
                 partial2(
-                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy_unit(t, v, n),
+                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy(t, v, n),
                     &self.volume,
                     &self.moles,
                 ),
@@ -111,7 +111,7 @@ where
         let ideal_gas = || {
             -quantity::ad::second_derivative(
                 partial2(
-                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy_unit(t, v, n),
+                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy(t, v, n),
                     &self.volume,
                     &self.moles,
                 ),
@@ -131,7 +131,7 @@ where
         let ideal_gas = || {
             -quantity::ad::third_derivative(
                 partial2(
-                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy_unit(t, v, n),
+                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy(t, v, n),
                     &self.volume,
                     &self.moles,
                 ),
@@ -165,8 +165,14 @@ where
     pub fn helmholtz_energy(&self, contributions: Contributions) -> Energy<D> {
         let residual = || self.residual_helmholtz_energy();
         let ideal_gas = || {
-            self.eos
-                .ideal_gas_helmholtz_energy_0(self.temperature, self.volume, &self.moles)
+            quantity::ad::zeroth_derivative(
+                partial2(
+                    |t, &v, n| self.eos.ideal_gas_helmholtz_energy(t, v, n),
+                    &self.volume,
+                    &self.moles,
+                ),
+                self.temperature,
+            )
         };
         Self::contributions(ideal_gas, residual, contributions)
     }

diff --git a/crates/feos-derive/src/ideal_gas.rs b/crates/feos-derive/src/ideal_gas.rs
@@ -42,7 +42,7 @@ fn impl_ideal_gas(
     });
     quote! {
         impl IdealGas for IdealGasModel {
-            fn ln_lambda3<D: DualNum<f64> + Copy>(&self, temperature: D) -> D {
+            fn ln_lambda3<D: DualNum<f64, Inner=f64> + Copy>(&self, temperature: D) -> D {
                 match self {
                     #(#ln_lambda3,)*
                 }

diff --git a/crates/feos/src/ideal_gas/joback.rs b/crates/feos/src/ideal_gas/joback.rs
@@ -1,13 +1,12 @@
 //! Implementation of the ideal gas heat capacity (de Broglie wavelength)
 //! of [Joback and Reid, 1987](https://doi.org/10.1080/00986448708960487).
 use feos_core::parameter::{FromSegments, Parameters};
-use feos_core::{FeosResult, IdealGas, IdealGasAD, ReferenceSystem};
+use feos_core::{FeosResult, IdealGas, ReferenceSystem};
 use nalgebra::DVector;
 use num_dual::*;
 use quantity::{MolarEntropy, Temperature};
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
-use std::ops::Mul;
 
 /// Coefficients used in the Joback model.
 ///
@@ -95,11 +94,11 @@ impl Joback {
             .sum();
         Ok(c_p / RGAS * quantity::RGAS)
     }
+}
 
-    fn ln_lambda3<D: DualNum<f64> + Copy + Mul<D1, Output = D>, D1: Copy>(
-        [a, b, c, d, e]: [D1; 5],
-        temperature: D,
-    ) -> D {
+impl<D: DualNum<f64> + Copy> IdealGas<D> for Joback<D> {
+    fn ln_lambda3<D2: DualNum<f64, Inner = D> + Copy>(&self, temperature: D2) -> D2 {
+        let [a, b, c, d, e] = self.0.each_ref().map(D2::from_inner);
         let t = temperature;
         let t2 = t * t;
         let t4 = t2 * t2;
@@ -116,12 +115,6 @@ impl Joback {
             + (t / T0).ln() * a;
         (h - t * s) / (t * RGAS) + f
     }
-}
-
-impl IdealGas for Joback {
-    fn ln_lambda3<D: DualNum<f64> + Copy>(&self, temperature: D) -> D {
-        Self::ln_lambda3(self.0, temperature)
-    }
 
     fn ideal_gas_model(&self) -> &'static str {
         "Ideal gas (Joback)"
@@ -166,20 +159,6 @@ impl<D: DualNum<f64> + Copy> Joback<D> {
     }
 }
 
-impl<D: DualNum<f64> + Copy> IdealGasAD<D> for Joback<D> {
-    fn ln_lambda3_ad<D2: DualNum<f64, Inner = D> + Copy>(&self, temperature: D2) -> D2 {
-        Joback::ln_lambda3(self.0.each_ref().map(D2::from_inner), temperature)
-    }
-
-    fn ln_lambda3(&self, temperature: D) -> D {
-        Joback::ln_lambda3(self.0, temperature)
-    }
-
-    fn ideal_gas_model(&self) -> &'static str {
-        "Ideal gas (Joback)"
-    }
-}
-
 const RGAS: f64 = 6.022140857 * 1.38064852;
 const T0: f64 = 298.15;
 const T0_2: f64 = T0 * T0;