Appendix B — Atlas Glossary

Figure B.2 — B. Glossary

A consolidated glossary spanning every Atlas crate that CFDrs, Helios, and Kwavers consume. Where a term has an Atlas-crate-specific meaning, the relevant crate is named in parentheses.

A

Alloc, Arena Allocation (mnemosyne). A type-erased memory region that owns its chunks and recycles them in O(1) on reset(). The Atlas default for transient solver storage.

Apollo (apollo). The Atlas forward-only FFT crate. Apollo exposes FftPlan::forward_real and forward_complex. Inverse FFT is done by forward + complex-conjugate.

Atlas Stack. The unified first-party mathematics, memory, SIMD, and concurrency stack that replaces ndarray/nalgebra/burn, tokio/rayon, packed_simd, rustfft, etc. Atlas crates span eunomia, leto, hephaestus, coeus, apollo, hermes-simd, mnemosyne, themis, moirai, ritk, and consus.

Autodiff / Autograd (coeus). Reverse-mode automatic differentiation. Coeus tracks an autodiff tape so that any Tensor<T> participates in a backward graph.

B

Backend (Compute) (hephaestus). A hephaestus::Backend is one of Cpu, Wgpu, or Cuda. Atlas consumers carry a backend as a type parameter so the same source compiles for any backend.

BoundaryType (cfd-core, helios-domain). A typed enum of boundary conditions (no-slip wall, lid, slip, partial-slip, etc.).

C

Carreau / Carreau-Yasuda / Casson / Power-law. Non-Newtonian blood rheology models in cfd-1d.

Coeus (coeus). Atlas tensor + autodiff crate. Equivalent to PyTorch/JAX/Burn from the Atlas perspective.

Compile-time dispatch. The Atlas technique of using #[cfg(target_arch)] + PhantomData so that the same source compiles to specialized code per (Scalar, Backend) pair, no virtual dispatch.

ComputeBackend. A eunomia::Backend is Cpu, Wgpu, or Cuda.

CowArray (leto). A Cow<'a, NdArray<T, D>> used for read-then-write slicing without cloning the underlying storage.

Cow (Copy-on-write). Atlas pattern for views that preferentially borrow; only copy when a write requires owning.

D

DICOM (ritk). Digital Imaging and Communications in Medicine. The standard medical-imaging format. Ritk parses DICOM into typed DicomElements.

DIF, DIP. Dependency-Inversion Principle: depend on traits (eunomia::RealField, moirai::Executor), not impls.

DRY. Don’t Repeat Yourself. Atlas enforces DRY at the trait frontier — there is one RealField, not five.

E

Eunomia (eunomia). Atlas numeric-trait crate that unifies num-traits + num-complex + custom precision types.

Executor (moirai). The unified async + parallel worker pool that replaces tokio::Runtime and rayon::ThreadPool.

F

FftPlan (apollo). A pre-computed FFT plan for a fixed shape. Used by every Atlas consumer running spectral methods.

FloatElement (eunomia). Atlas trait bound for floating-point scalars that want Atlas-wide opt-in to SIMD / autodiff / MPI.

Foundations (kwavers/cfd-core/helios-core). The lowest chapter / layer: type definitions, validation contracts, dimension checking.

G

GAT — Generic Associated Type (Rust). A type-level parameter on a trait. Atlas uses a GAT for leto_ops::StatefulUpdateRule::State<'a>, whose mutable state-view family is re-parameterized per lifetime by each update rule.

GpuArray / GpuBackend (hephaestus). The GPU-side counterpart of leto::NdArray and eunomia::ComputeBackend.

H

Hephaestus (hephaestus). The Atlas GPU crate — wgpu (cross- platform) and CUDA backends.

Hermes (hermes-simd). The Atlas SIMD crate with portable SSE2 / AVX2 / AVX-512 / NEON / WASM lane dispatch.

Host–Device Sync. The boundary between leto (CPU) and hephaestus (GPU). Sync is mediated by hephaestus::sync_* functions; Atlas arrays can flow across it with explicit to_device() / to_host().

I

Isometry3 (leto). A 3-D rigid transformation (rotation + translation). Equivalent to nalgebra::Isometry3, but uses Leto’s quaternion representation.

Ix1..IxN (leto). Const-generic dimension types for multi-dimensional arrays.

K

KernelCache (hephaestus). Pre-compiled shader / CUDA kernels, keyed by (shape, dtype). Avoids recompilation on every launch.

Krylov solver (cfd-math, coeus). An iterative linear solver (BiCGSTAB, GMRES, IDR(s)) that needs only apply(A, x) for the matrix-free path.

L

Lending Iterator. An Atlas iterator that yields a value whose lifetime is shorter than &self — encoded via type Item<'a>. See Rust RFC 1598.

Leto (leto). Atlas CPU dense/sparse storage crate — NdArray<T, D>, CowArray<'a, T, D>, CsrMatrix<T>, DMatrix<T>, and the geometry types Point3<T>, Vector3<T>, Isometry3<T>.

LtoArray / LtoView (leto). Aliases for NdArray and CowArray respectively, used in adjoint passes.

M

MatrixFree (cfd-math, apollo). An operator-application pattern where the linear operator is a trait and the solver allocates only the action A·x.

Migration Reference. The Atlas-stack migration chapter in each of the three books (CFDrs Part VII, Helios Part VIII, Kwavers Part VI).

Mnemosyne (mnemosyne). Atlas arena allocator crate — Arena, ScratchArena, with chunked growth.

Moirai (moirai). Atlas async + parallel crate. Replaces tokio::Runtime + rayon::ThreadPool.

Moiraiexecutor (moirai). The runtime type that spawns futures and dispatches parallel work.

N

NdArray (leto). Atlas dense n-dimensional array. Replaces ndarray::Array* and nalgebra::DMatrix/Tensor.

NUMA Placement (themis). Per-Arena binding to a physical core or NUMA node — see Placement::bind_to, Placement::numa_aware.

P

PhantomData. Zero-sized marker type that forces the Rust compiler to honour capability requirements. Atlas uses PhantomData<F>, PhantomData<B>, PhantomData<(F, B)> to tie scalar type and backend to every struct.

PyO3 boundary (cfd-python, helios-python, kwavers-python). Atlas Rust ↔ Python boundary. All cross-boundary types must implement IntoPyObject and FromPyObject.

R

Rayleigh–Plesset (cfd-3d::cavitation). Single-bubble cavitation ODE. Atlas’ default cavitation model.

RealField (eunomia). Atlas trait bound for any floating-point-real-type. The minimum surface that numeric Atlas consumers must implement.

Ritk (ritk). Atlas image-toolkit crate — DICOM, PNG, NIfTI.

S

SIMD Lane (hermes-simd). A SimdLane-implementing type (Avx2Lane<F>, Avx512Lane<F>, …). Used in vectorized kernels.

Spectral Tile (apollo, leto). A frequency-domain partition struct used by tiled spectral solvers.

SRP. Single Responsibility Principle — each Atlas crate owns one well-defined surface.

SSOT. Single Source of Truth — every Atlas capability lives in exactly one crate.

Spectral FFT (apollo, cfd-3d::spectral). The Atlas FFT pipeline (Apollo forward FFT + Atlas autodiff tape).

T

TaskGraph (moirai). A DAG of dependent compute tasks, executed by an Executor. Replaces rayon::join, tokio::join, and ad-hoc thread pools.

Tensor (coeus). An autodiff-aware n-dimensional array.

Themis (themis). Atlas NUMA / physical-core placement crate. Bind Arena chunks to NUMA nodes so that solver reads land cache-hot.

TileStreaming (leto). A trait with a GAT-based iterator that yields &Tile<'a> over an Atlas volume.

Typed Boundary. A CFD boundary condition carried by cfd_core::physics::boundary::BoundaryCondition<T> variants such as VelocityInlet, PressureOutlet, and Wall, rather than by runtime string tags.

Z

Zero-Copy. Atlas pattern: every read-only consumer takes Cow<'_, T> instead of T, so the underlying storage is shared when no write is needed.

Zero-Cost Abstraction. Atlas pattern: every abstraction (ZSTs, GATs, PhantomData, const generics) compiles away to zero cycles per call site.

ZST. Zero-Sized Type. Atlas uses PhantomData<F> and similar ZSTs to encode capability at compile time without runtime cost.