Added equinoctial elements. Also a little cleanup

benches/kepler.rs

@@ -8,6 +8,7 @@ use std::hint::black_box;
 
 use astrokit::body::Body;
 use astrokit::cartesian::Cartesian;
+use astrokit::equinoctial::Equinoctial;
 use astrokit::frames::Frame;
 use astrokit::kepler::{self, Degeneracy, Keplerian};
 use criterion::{criterion_group, criterion_main, Criterion};
@@ -121,11 +122,44 @@ fn bench_invariants(c: &mut Criterion) {
     group.finish();
 }
 
+/// Equinoctial against Keplerian on the same states.
+///
+/// The interesting comparison is GEO: Keplerian takes its doubly-degenerate
+/// branch there and equinoctial takes no branch at all.
+fn bench_equinoctial(c: &mut Criterion) {
+    let mut group = c.benchmark_group("equinoctial");
+
+    let leo = leo();
+    let geo = geo();
+
+    group.bench_function("from_cartesian/leo", |b| {
+        b.iter(|| Equinoctial::from_cartesian(&black_box(leo)))
+    });
+    group.bench_function("from_cartesian/geo", |b| {
+        b.iter(|| Equinoctial::from_cartesian(&black_box(geo)))
+    });
+
+    let elements = Equinoctial::from_cartesian(&leo);
+    group.bench_function("to_cartesian", |b| {
+        b.iter(|| black_box(elements).to_cartesian())
+    });
+    group.bench_function("round_trip", |b| {
+        b.iter(|| Equinoctial::from_cartesian(&black_box(leo)).to_cartesian())
+    });
+
+    let keplerian = leo.keplerian();
+    group.bench_function("from_keplerian", |b| {
+        b.iter(|| Equinoctial::from_keplerian(&black_box(keplerian)))
+    });
+    group.finish();
+}
+
 criterion_group!(
     benches,
     bench_scalar_relations,
     bench_anomalies,
     bench_conversions,
-    bench_invariants
+    bench_invariants,
+    bench_equinoctial
 );
 criterion_main!(benches);

benches/propagation.rs

@@ -117,9 +117,9 @@ fn bench_one_period(c: &mut Criterion) {
 
 /// The cost of a state transition matrix relative to a plain propagation.
 ///
-/// Stage 1 measured 10.6x for a 6x6 on a two-body arc. Central differences would
-/// need thirteen propagations and lose about half the digits, so anything near
-/// that ratio is a win; this tracks it as the force models get heavier.
+/// Central differences would need thirteen propagations for a 6x6 and lose about
+/// half the available digits. This tracks the ratio as the force models get
+/// heavier.
 #[cfg(feature = "autodiff")]
 fn bench_state_transition_matrix(c: &mut Criterion) {
     use nalgebra::{Matrix6, Vector6};