Spherical Harmonics in Rust

Cargo.toml

@@ -18,7 +18,7 @@ members = ["benchmarks",
            "hoomd-vector",
            "tools/build-wasm-doc-examples",
            "hoomd-rand"
-          ]
+          , "hoomd-order"]
 
 # Include only core hoomd simulation crates by default so that `cargo build`,
 # `cargo test` and similar commands operate only on the core code by default.
@@ -74,6 +74,7 @@ assert2 = "=0.4.0"
 divan = "=0.1.21"
 paste = "=1.0.15"
 rand_sfc = "=0.2.0"
+sphrs = "=0.2.2"
 rstest = "=0.26.1"
 tempfile = "=3.27.0"
 strum = "=0.28.0"
@@ -97,9 +98,10 @@ parquet_derive = { version = "58.0.0", default-features=false }
 
 # Dependencies exposed via Public APIs.
 anyhow = "1.0.100"
-approxim = "0.6.6"
+approxim = {version = "0.6.6", features = ["num-complex"]}
 arrayvec = { version = "0.7.6", features = ["serde"] }
 num = { version = "0.4.3", features = ["serde"] }
+num-complex = "0.4"
 rand = { version = "0.10.0", default-features=false, features = ["std", "std_rng"] }
 serde = { version = "1.0.228", features = ["derive"]}
 thiserror = "2.0.12"

hoomd-order/Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+name = "hoomd-order"
+description = "Evaluate Spherical Harmonics at a given Cartesian point."
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+homepage.workspace = true
+documentation.workspace = true
+repository.workspace = true
+license.workspace = true
+keywords.workspace = true
+categories.workspace = true
+
+[dependencies]
+hoomd-vector = "1.1.0"
+num-complex.workspace = true
+
+[dev-dependencies]
+approxim.workspace = true
+divan.workspace = true
+rand.workspace = true
+rstest.workspace = true
+sphrs.workspace = true
+
+[lints]
+workspace = true
+
+[[bench]]
+name = "harmonics"
+harness = false

hoomd-order/README.md

@@ -0,0 +1,5 @@
+# hoomd-order
+
+Order parameter analysis library for [hoomd-rs].
+
+[hoomd-rs]: https://github.com/glotzerlab/hoomd-rs

hoomd-order/benches/harmonics.rs

@@ -0,0 +1,34 @@
+// Copyright (c) 2024-2026 The Regents of the University of Michigan.
+// Part of hoomd-rs, released under the BSD 3-Clause License.
+
+//! ...
+use hoomd_order::SphericalHarmonic;
+use hoomd_vector::{Cartesian, InnerProduct};
+use rand::{Rng, RngExt, SeedableRng, rngs::StdRng};
+
+/// Generate a random point on the unit sphere.
+#[inline]
+fn random_unit_point<R: Rng>(rng: &mut R) -> Cartesian<3> {
+    let (x, y, z) = (rng.random(), rng.random(), rng.random());
+    Cartesian::from([x, y, z])
+}
+fn main() {
+    divan::main();
+}
+
+/// Measure per-point performance at each l.
+#[divan::bench(
+    consts = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
+    sample_count = 1_000,
+    sample_size = 10_000,
+)]
+fn recurrence<const L: usize>(bencher: divan::Bencher<'_, '_>) {
+    let sh = SphericalHarmonic::<L>::new();
+    let mut rng = StdRng::seed_from_u64(1);
+    bencher
+        .with_inputs(|| {
+            let point = random_unit_point::<StdRng>(&mut rng);
+            (point.to_unit().expect("non-zero point")).0
+        })
+        .bench_local_values(|xyz| sh.eval(xyz));
+}