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prehner merged 3 commits into from
Jan 28, 2023
Merged

Fix association contribution for some association schemes and improve performance #129

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b82c32f
Fix association contribution for some association schemes and improve…
prehner Jan 27, 2023
6c51854
add changelog entry
prehner Jan 27, 2023
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update version
prehner Jan 28, 2023
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Fix association contribution for some association schemes and improve… 
… performance
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@prehner
prehner committed Jan 27, 2023
commit b82c32f3f7c79bbd156a0c5f0ce345d73306a6b3
54 changes: 36 additions & 18 deletions src/association/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ use num_dual::linalg::{norm, LU};
use num_dual::*;
use serde::{Deserialize, Serialize};
use std::fmt;
use std::ops::SubAssign;
use std::sync::Arc;

#[cfg(feature = "dft")]
Expand Down Expand Up @@ -243,7 +244,7 @@ impl<P: HardSphereProperties> Association<P> {
(((deltarho * (na - nb) + 1.0).powi(2) + deltarho * nb * 4.0).sqrt()
+ (deltarho * (nb - na) + 1.0))
.recip()
* (2.0 * nb / na)
* 2.0
}

pub fn assoc_site_frac_a<D: DualNum<f64>>(deltarho: D, na: f64) -> D {
Expand Down Expand Up @@ -336,37 +337,32 @@ impl<P: HardSphereProperties> Association<P> {
tol: f64,
) -> Result<bool, EosError> {
// gradient
let mut g: Array1<D> = Array::zeros(2 * nassoc);
let mut g = x.map(D::recip);
// Hessian
let mut h: Array2<D> = Array::zeros((2 * nassoc, 2 * nassoc));

// slice arrays
let (xa, xb) = x.multi_slice_mut((s![..nassoc], s![nassoc..]));
let (mut ga, mut gb) = g.multi_slice_mut((s![..nassoc], s![nassoc..]));
let (mut haa, mut hab, mut hba, mut hbb) = h.multi_slice_mut((
s![..nassoc, ..nassoc],
s![..nassoc, nassoc..],
s![nassoc.., ..nassoc],
s![nassoc.., nassoc..],
));
// split x array
let (xa, xb) = x.view().split_at(Axis(0), nassoc);

// calculate gradients and approximate Hessian
for i in 0..nassoc {
let d = &delta.index_axis(Axis(0), i) * rho;

let dnx = (&xb * nb * &d).sum() + 1.0;
ga[i] = xa[i].recip() - dnx;
hab.index_axis_mut(Axis(0), i).assign(&(&d * &(-nb)));
haa[(i, i)] = -dnx / xa[i];
g[i] -= dnx;
for j in 0..nassoc {
h[(i, nassoc + j)] = -d[j] * nb[j];
h[(nassoc + i, j)] = -d[j] * na[j];
}
h[(i, i)] = -dnx / xa[i];

let dnx = (&xa * na * &d).sum() + 1.0;
gb[i] = xb[i].recip() - dnx;
hba.index_axis_mut(Axis(0), i).assign(&(&d * &(-na)));
hbb[(i, i)] = -dnx / xb[i];
g[nassoc + i] -= dnx;
h[(nassoc + i, nassoc + i)] = -dnx / xb[i];
}

// Newton step
x.assign(&(&*x - &LU::new(h)?.solve(&g)));
x.sub_assign(&LU::new(h)?.solve(&g));

// check convergence
Ok(norm(&g.map(D::re)) < tol)
Expand All @@ -378,7 +374,9 @@ impl<P: HardSphereProperties> Association<P> {
mod tests_pcsaft {
use super::*;
use crate::pcsaft::parameters::utils::water_parameters;
use crate::pcsaft::PcSaftParameters;
use approx::assert_relative_eq;
use feos_core::parameter::Parameter;

#[test]
fn helmholtz_energy() {
Expand All @@ -403,6 +401,26 @@ mod tests_pcsaft {
let a_rust = assoc.helmholtz_energy(&s) / n;
assert_relative_eq!(a_rust, -4.229878997054543, epsilon = 1e-10);
}

#[test]
fn helmholtz_energy_cross_3b() {
let mut params = water_parameters();
let mut record = params.pure_records.pop().unwrap();
let mut association_record = record.model_record.association_record.unwrap();
association_record.na = Some(2.0);
record.model_record.association_record = Some(association_record);
let params = Arc::new(PcSaftParameters::new_pure(record));
let assoc = Association::new(&params, &params.association, 50, 1e-10);
let cross_assoc =
Association::new_cross_association(&params, &params.association, 50, 1e-10);
let t = 350.0;
let v = 41.248289328513216;
let n = 1.23;
let s = StateHD::new(t, v, arr1(&[n]));
let a_assoc = assoc.helmholtz_energy(&s) / n;
let a_cross_assoc = cross_assoc.helmholtz_energy(&s) / n;
assert_relative_eq!(a_assoc, a_cross_assoc, epsilon = 1e-10);
}
}

#[cfg(test)]
Expand Down