la_stack/

lib.rs

#![forbid(unsafe_code)]
#![deny(missing_docs)]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![doc = include_str!("../README.md")]

#[cfg(doc)]
mod readme_doctests {
    //! Executable version of the README quickstart.
    /// ```rust
    /// use la_stack::prelude::*;
    ///
    /// fn main() -> Result<(), LaError> {
    ///     // The zero leading entry requires LU pivoting.
    ///     let a = Matrix::<5>::try_from_rows([
    ///         [0.0, 2.0, -1.0, 1.0, 3.0],
    ///         [4.0, -1.0, 2.0, 0.0, 1.0],
    ///         [1.0, 3.0, 5.0, -2.0, 0.0],
    ///         [2.0, 0.0, -1.0, 4.0, 1.0],
    ///         [-1.0, 2.0, 0.0, 1.0, 6.0],
    ///     ])?;
    ///     let b = Vector::try_new([20.0, 13.0, 14.0, 20.0, 37.0])?;
    ///     let lu = a.lu(DEFAULT_SINGULAR_TOL)?;
    ///     let x = lu.solve(b)?;
    ///
    ///     for (&actual, expected) in x.as_array().iter().zip([1.0, 2.0, 3.0, 4.0, 5.0]) {
    ///         assert!((actual - expected).abs() <= 1e-12);
    ///     }
    ///     Ok(())
    /// }
    /// ```
    fn solve_5x5_example() {}
}

// Documentation-only workflows keep the README overview compact without adding
// a runtime API. Their examples are executed by the default/exact doctest gates.
#[cfg(doc)]
pub mod guide {
    //! Worked examples and contracts for choosing and combining APIs.
    //!
    //! Start with [`prelude`](crate::prelude) for common imports. The crate's
    //! generated reference lists the complete public surface; these examples
    //! demonstrate how the pieces fit together.
    //!
    //! Explore the topic guides for more workflows:
    //!
    //! - [LDLT determinants and symmetry](ldlt)
    //! - [Compile-time determinants](compile_time)
    //! - [Outward-rounded interval determinants](intervals)
    //! - [Overflow-safe Euclidean norms](norms)
    //! - [Certified dot products and affine differences](certified)
    //! - [Adaptive determinant filtering](adaptive)
    //!
    //! Enabling `exact` also adds the exact-arithmetic guide to the module list.
    //!
    //! # Solving and reusing factors
    //!
    //! [`Matrix::lu`](crate::Matrix::lu) computes a partially pivoted
    //! factorization. Keep the resulting [`Lu`](crate::Lu) to solve multiple
    //! right-hand sides without repeating factorization. This 5×5 system has a
    //! zero leading entry, so the first elimination step requires pivoting.
    //!
    //! ```rust
    //! use la_stack::prelude::*;
    //!
    //! # fn main() -> Result<(), LaError> {
    //! let a = Matrix::<5>::try_from_rows([
    //!     [0.0, 2.0, -1.0, 1.0, 3.0],
    //!     [4.0, -1.0, 2.0, 0.0, 1.0],
    //!     [1.0, 3.0, 5.0, -2.0, 0.0],
    //!     [2.0, 0.0, -1.0, 4.0, 1.0],
    //!     [-1.0, 2.0, 0.0, 1.0, 6.0],
    //! ])?;
    //! let lu = a.lu(DEFAULT_SINGULAR_TOL)?;
    //! let systems = [
    //!     ([20.0, 13.0, 14.0, 20.0, 37.0], [1.0, 2.0, 3.0, 4.0, 5.0]),
    //!     ([5.0, 6.0, 7.0, 6.0, 8.0], [1.0; 5]),
    //! ];
    //! for (rhs, expected) in systems {
    //!     let solution = lu.solve(Vector::try_new(rhs)?)?;
    //!     for (&actual, expected) in solution.as_array().iter().zip(expected) {
    //!         assert!((actual - expected).abs() <= 1e-12);
    //!     }
    //! }
    //! # Ok(())
    //! # }
    //! ```
    //!
    //! The assertions use a tolerance suitable for this known fixture; they do
    //! not establish a general error bound for LU. Factorization tolerances
    //! reject small pivots and are not accuracy guarantees.
    //! [`Ldlt`](crate::Ldlt) offers the same solve/determinant workflow for
    //! exactly symmetric positive-definite input, without pivoting. Approximate
    //! symmetry from [`Matrix::is_symmetric`](crate::Matrix::is_symmetric) or
    //! [`Matrix::first_asymmetry`](crate::Matrix::first_asymmetry) does not prove
    //! the exact symmetry required by [`Matrix::ldlt`](crate::Matrix::ldlt).
    //!
    //! # Gram matrices
    //!
    //! [`gram_matrix`](crate::gram_matrix) accepts `M` vectors of dimension `N`
    //! and returns a `Matrix<M>` of pairwise inner products. Here five vectors
    //! in six dimensions produce a 5×5 matrix. Each dot product is computed once
    //! and mirrored, so the result is bit-for-bit symmetric.
    //!
    //! ```rust
    //! use la_stack::prelude::*;
    //!
    //! # fn main() -> Result<(), LaError> {
    //! let vectors = [
    //!     Vector::try_new([1.0, 1.0, 0.0, 0.0, 0.0, 0.0])?,
    //!     Vector::try_new([0.0, 1.0, 1.0, 0.0, 0.0, 0.0])?,
    //!     Vector::try_new([0.0, 0.0, 1.0, 1.0, 0.0, 0.0])?,
    //!     Vector::try_new([0.0, 0.0, 0.0, 1.0, 1.0, 0.0])?,
    //!     Vector::try_new([0.0, 0.0, 0.0, 0.0, 1.0, 1.0])?,
    //! ];
    //! let gram = gram_matrix(&vectors)?;
    //! assert_eq!(gram.norm_inf()?, 4.0);
    //! assert!(gram.is_symmetric(Tolerance::try_new(0.0)?)?);
    //!
    //! // This fixture's exact Gram matrix is tridiagonal: 2 on the diagonal,
    //! // 1 immediately above/below it. Its 5×5 determinant is 6.
    //! let determinant = gram.ldlt(DEFAULT_SINGULAR_TOL)?.det()?;
    //! assert!((determinant - 6.0).abs() <= 1e-12);
    //! # Ok(())
    //! # }
    //! ```
    //!
    //! Gram construction provides no certified rounding-error bound and does
    //! not prove rank or positive definiteness. The generated function
    //! documentation explains its conditioning and geometric interpretation.
    //!
    //! # Dimension dispatch
    //!
    //! [`try_with_stack_matrix!`](crate::try_with_stack_matrix) selects a
    //! concrete `Matrix<N>` for runtime dimensions 0 through
    //! [`MAX_STACK_MATRIX_DISPATCH_DIM`](crate::MAX_STACK_MATRIX_DISPATCH_DIM)
    //! (7). The closure receives a zero matrix and returns its declared result.
    //!
    //! ```rust
    //! use core::assert_matches;
    //!
    //! use la_stack::prelude::*;
    //!
    //! # fn main() -> Result<(), LaError> {
    //! let requested = 5usize;
    //! let determinant = try_with_stack_matrix!(requested, |mut matrix| -> Result<f64, LaError> {
    //!     for row in 0..requested {
    //!         matrix.set(row, row, 2.0)?;
    //!         if row + 1 < requested {
    //!             matrix.set(row, row + 1, 1.0)?;
    //!             matrix.set(row + 1, row, 1.0)?;
    //!         }
    //!     }
    //!     matrix.det()
    //! })?;
    //! assert!((determinant - 6.0).abs() <= 1e-12);
    //!
    //! let unsupported = try_with_stack_matrix!(8, |matrix| -> Result<f64, LaError> {
    //!     matrix.det()
    //! });
    //! assert_matches!(
    //!     unsupported,
    //!     Err(LaError::UnsupportedDimension { requested: 8, max: 7, .. })
    //! );
    //! # Ok(())
    //! # }
    //! ```
    //!
    //! [`try_with_interval_matrix!`](crate::try_with_interval_matrix) similarly
    //! dispatches dimensions 0 through
    //! [`MAX_INTERVAL_MATRIX_DIM`](crate::MAX_INTERVAL_MATRIX_DIM) (7) to an
    //! [`IntervalMatrix`](crate::IntervalMatrix). These macros are useful when
    //! stable Rust cannot express a derived const dimension such as `D + 1`.
    //! Larger dimensions produce [`LaError::UnsupportedDimension`](crate::LaError::UnsupportedDimension),
    //! converted through `From<LaError>` into the closure's declared error type.
    //! Dispatch preserves const-generic storage; it does not create a dynamically
    //! sized matrix representation or limit dimensions chosen directly at compile time.
    //!
    //! # Storage, access, and errors
    //!
    //! [`Matrix<D>`](crate::Matrix) and [`Vector<D>`](crate::Vector) store
    //! `[[f64; D]; D]` and `[f64; D]` inline. Constructors validate non-finite
    //! inputs, and the types preserve that finite-storage invariant. Factorization
    //! kernels therefore avoid a repeated O(D²) input scan; computed factor
    //! matrices are still checked before becoming observable results.
    //!
    //! [`Matrix::as_rows`](crate::Matrix::as_rows) and
    //! [`Vector::as_array`](crate::Vector::as_array) borrow validated backing
    //! arrays. [`Matrix::into_rows`](crate::Matrix::into_rows) and
    //! [`Vector::into_array`](crate::Vector::into_array) consume the value and
    //! return owned fixed-size arrays.
    //! [`Matrix::get`](crate::Matrix::get) returns `None` for invalid coordinates;
    //! [`Matrix::try_get`](crate::Matrix::try_get) preserves them in a typed error.
    //! [`Matrix::set`](crate::Matrix::set) checks coordinates and finiteness
    //! before mutation. [`Matrix::norm_inf`](crate::Matrix::norm_inf) computes
    //! the maximum absolute row sum.
    //!
    //! [`Vector::dot`](crate::Vector::dot), [`Vector::norm`](crate::Vector::norm),
    //! and [`Vector::norm_squared`](crate::Vector::norm_squared) provide ordinary
    //! vector reductions. [`ScalarWithErrorBound`](crate::ScalarWithErrorBound)
    //! is the opaque result of the certified dot and affine-difference methods;
    //! it exposes the estimate, absolute bound, and outward-rounded endpoints.
    //! [`DeterminantWithErrorBound`](crate::DeterminantWithErrorBound) pairs a
    //! direct determinant with its certified absolute bound. Use
    //! [`Matrix::det_errbound`](crate::Matrix::det_errbound) for the bound alone.
    //!
    //! [`Interval`](crate::Interval) stores two finite ordered bounds and supports
    //! point construction, outward-rounded subtraction, addition, multiplication,
    //! negation, and square. [`IntervalMatrix`](crate::IntervalMatrix) stores
    //! `[[Interval; D]; D]` inline and uses a fixed 128-entry stack workspace for
    //! supported determinant dimensions. [`IntervalDeterminantSign`](crate::IntervalDeterminantSign)
    //! distinguishes positive, negative, exact zero, and inconclusive evidence.
    //!
    //! Parse numerical thresholds through [`Tolerance::try_new`](crate::Tolerance::try_new).
    //! [`LaError`](crate::LaError) and its reason/location enums are non-exhaustive;
    //! use wildcard match arms and `..` for struct-style variants. In particular:
    //!
    //! - [`SingularityReason`](crate::SingularityReason) separates exact singularity
    //!   from numerical rejection, retaining the [`FactorizationKind`](crate::FactorizationKind),
    //!   observed pivot magnitude, and tolerance for the latter.
    //! - [`NonFiniteOrigin`](crate::NonFiniteOrigin), [`NonFiniteLocation`](crate::NonFiniteLocation),
    //!   and [`ArithmeticOperation`](crate::ArithmeticOperation) distinguish invalid
    //!   inputs from computed non-finite values.
    //! - [`LaError::InvertedInterval`](crate::LaError::InvertedInterval) preserves
    //!   rejected finite endpoints; [`LaError::IntervalRangeExhausted`](crate::LaError::IntervalRangeExhausted)
    //!   distinguishes finite-input interval range loss from a non-finite value.
    //! - [`InvalidToleranceReason`](crate::InvalidToleranceReason) distinguishes
    //!   negative and non-finite tolerances.
    //! - [`PositiveSemidefiniteViolation`](crate::PositiveSemidefiniteViolation)
    //!   distinguishes a negative LDLT pivot from a zero pivot with nonzero coupling.

    pub mod ldlt {
        //! LDLT determinants and exact symmetry.
        //!
        //! Compute a determinant for a symmetric positive-definite matrix via LDLT (no
        //! pivoting).
        //!
        //! For these matrices, `LDLᵀ` is a square-root-free Cholesky form. Multiplying each
        //! column of `L` by the square root of the corresponding diagonal entry yields a
        //! Cholesky factor:
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! fn main() -> Result<(), LaError> {
        //!     // This matrix is symmetric positive-definite (A = L*L^T) so LDLT works without pivoting.
        //!     let a = Matrix::<5>::try_from_rows([
        //!         [1.0, 1.0, 0.0, 0.0, 0.0],
        //!         [1.0, 2.0, 1.0, 0.0, 0.0],
        //!         [0.0, 1.0, 2.0, 1.0, 0.0],
        //!         [0.0, 0.0, 1.0, 2.0, 1.0],
        //!         [0.0, 0.0, 0.0, 1.0, 2.0],
        //!     ])?;
        //!
        //!     let ldlt = match a.ldlt(DEFAULT_SINGULAR_TOL) {
        //!         Ok(ldlt) => ldlt,
        //!         Err(err @ LaError::Asymmetric {
        //!             row,
        //!             col,
        //!             upper,
        //!             lower,
        //!             allowed_abs_diff,
        //!             ..
        //!         }) => {
        //!             eprintln!(
        //!                 "LDLT mismatch at ({row}, {col}): {upper} vs {lower} (allowed {allowed_abs_diff})"
        //!             );
        //!             return Err(err);
        //!         }
        //!         Err(err) => return Err(err),
        //!     };
        //!
        //!     let det = ldlt.det()?;
        //!     assert!((det - 1.0).abs() <= 1e-12);
        //!
        //!     Ok(())
        //! }
        //! ```
        //!
        //! > ⚠️ **LDLT invariant:** The input matrix must be **exactly symmetric**: every
        //! > mirrored pair must compare equal (`+0.0 == -0.0` is accepted). Asymmetric
        //! > inputs passed to
        //! > [`Matrix::ldlt`](crate::Matrix::ldlt)
        //! > return a typed `LaError::Asymmetric` containing both observed values and the
        //! > required allowed difference of zero. The tolerance-based
        //! > [`Matrix::first_asymmetry`](crate::Matrix::first_asymmetry)
        //! > and [`Matrix::is_symmetric`](crate::Matrix::is_symmetric) methods remain useful diagnostics, but do not prove
        //! > the exact precondition required by LDLT. Use `lu()` when exact symmetry or
        //! > positive definiteness is not guaranteed. A negative LDLT diagonal or a zero
        //! > diagonal with nonzero remaining coupling returns
        //! > `LaError::NotPositiveSemidefinite` with a typed
        //! > `PositiveSemidefiniteViolation`. An uncoupled zero or positive pivot
        //! > at or below the caller's tolerance returns `LaError::Singular` with a
        //! > numerical `SingularityReason`. Because these pivots are computed in binary64,
        //! > success is not an exact positive-definiteness certificate for the stored
        //! > matrix.
    }

    pub mod compile_time {
        //! Compile-time determinants and dimension dispatch.
        //!
        //! [`det_direct()`](crate::Matrix::det_direct) is a `const fn` providing closed-form determinants for D=0–4,
        //! using fused multiply-add where applicable. It returns `Ok(Some(det))` for those
        //! dimensions and `Ok(None)` for D ≥ 5. `Matrix::<0>::zero().det_direct()` returns
        //! `Ok(Some(1.0))` (the empty-product convention). For D=1–4, direct formulas
        //! bypass LU factorization entirely. This enables compile-time evaluation when
        //! inputs are known:
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! // Evaluated entirely at compile time — no runtime cost.
        //! const DET: Result<Option<f64>, LaError> = match Matrix::<4>::try_from_rows([
        //!     [2.0, 0.0, 0.0, 0.0],
        //!     [0.0, 3.0, 0.0, 0.0],
        //!     [0.0, 0.0, 5.0, 0.0],
        //!     [0.0, 0.0, 0.0, 7.0],
        //! ]) {
        //!     Ok(matrix) => matrix.det_direct(),
        //!     Err(err) => Err(err),
        //! };
        //!
        //! fn main() -> Result<(), LaError> {
        //!     assert_eq!(DET?, Some(210.0));
        //!     Ok(())
        //! }
        //! ```
        //!
        //! The public `det()` method automatically dispatches through the closed-form path
        //! for D ≤ 4 and falls back to zero-tolerance LU for D ≥ 5. Tiny nonzero
        //! determinants are not flattened by a configured pivot tolerance. The LU fallback
        //! returns `LaError::Singular` when floating-point elimination cannot produce a
        //! non-zero pivot; it does not misreport that numerical failure as an exact zero.
        //! Use `lu()` directly when you need a different tolerance policy, and use the
        //! exact determinant APIs when exact singularity classification matters.
    }

    pub mod intervals {
        //! Outward-rounded interval expressions and determinant signs.
        //!
        //! `Interval` encloses expression construction that has not yet been reduced to a
        //! single stored `f64`. Point intervals preserve finite binary64 values exactly;
        //! `try_from_subtraction`, `try_add`, `try_mul`, `negate`, and `try_square` enclose
        //! the corresponding exact-real operations. [`IntervalMatrix<D>::det_sign()`](crate::IntervalMatrix::det_sign) then
        //! uses a division-free subset expansion through D=7, returning positive,
        //! negative, zero, or inconclusive evidence.
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! fn main() -> Result<(), LaError> {
        //!     // Relative coordinates and the lifted norm retain their construction error.
        //!     let x = Interval::try_from_subtraction(0.1, 0.0)?;
        //!     let y = Interval::try_from_subtraction(0.1, 0.0)?;
        //!     let z = Interval::try_from_subtraction(0.1, 0.0)?;
        //!     let lifted = x
        //!         .try_square()?
        //!         .try_add(&y.try_square()?)?
        //!         .try_add(&z.try_square()?)?;
        //!
        //!     let matrix = IntervalMatrix::<4>::from_rows([
        //!         [Interval::ONE, Interval::ZERO, Interval::ZERO, Interval::ONE],
        //!         [Interval::ZERO, Interval::ONE, Interval::ZERO, Interval::ONE],
        //!         [Interval::ZERO, Interval::ZERO, Interval::ONE, Interval::ONE],
        //!         [x, y, z, lifted],
        //!     ]);
        //!     assert_eq!(
        //!         matrix.det_sign()?,
        //!         IntervalDeterminantSign::Negative,
        //!     );
        //!     Ok(())
        //! }
        //! ```
        //!
        //! Every successful interval keeps finite ordered endpoints. Subnormal bounds are
        //! preserved, both signed zeros are treated as real zero and canonicalized to
        //! `+0.0`, and underflowed nonzero products widen toward the least subnormal value.
        //! If an exact result range cannot fit between finite binary64 endpoints, the
        //! operation returns `LaError::IntervalRangeExhausted` with its interval operation
        //! recorded in `ArithmeticOperation`.
        //!
        //! `Positive`, `Negative`, and `Zero` are proofs. `Inconclusive` only means that
        //! the determinant enclosure overlaps zero; it must not be converted to equality
        //! or singularity. A filtered-exact caller should rebuild the same derived
        //! expression with `RationalMatrix` and call `det_sign()` when the interval result
        //! is inconclusive or reports range failure. Lifting a finished `Matrix` with
        //! [`IntervalMatrix::from_matrix`](crate::IntervalMatrix::from_matrix) encloses its stored entries, but cannot recover
        //! rounding that occurred while those entries were assembled.
    }

    pub mod norms {
        //! Overflow-safe Euclidean norms and squared norms.
        //!
        //! `Vector::norm()` computes the Euclidean norm with a deterministic scaled
        //! sum-of-squares recurrence, so large or subnormal finite coordinates do not fail
        //! merely because their raw squares overflow or underflow. It returns positive zero
        //! for empty and all-zero vectors and reports `LaError::NonFinite` with
        //! `ArithmeticOperation::VectorNorm` only when the exact norm rounds to infinity.
        //! Near the upper range, a fixed-size stack accumulator sums squares exactly and
        //! compares squared rounding midpoints to prevent false or hidden overflow. This
        //! fallback needs no optional dependencies. The general binary64 result remains
        //! approximate and has no certified error bound.
        //!
        //! `Vector::norm_squared()` remains the direct left-to-right FMA sum of squares for
        //! callers that need the squared norm. Its distinct contract deliberately reports
        //! overflow when that square is not finite, even when `norm()` can return a finite
        //! norm.
        //!
        //! # Large and subnormal coordinates
        //!
        //! ```rust
        //! use core::assert_matches;
        //!
        //! use la_stack::prelude::*;
        //!
        //! # fn main() -> Result<(), LaError> {
        //! let large = Vector::<5>::try_new([3e200, 4e200, 0.0, 0.0, 0.0])?;
        //! assert!((large.norm()? / 1e200 - 5.0).abs() <= 1e-12);
        //! assert_matches!(
        //!     large.norm_squared(),
        //!     Err(LaError::NonFinite {
        //!         origin: NonFiniteOrigin::Computation {
        //!             operation: ArithmeticOperation::VectorSquaredNorm, ..
        //!         },
        //!         location: NonFiniteLocation::Step { index: 0, .. },
        //!         ..
        //!     })
        //! );
        //!
        //! let tiny = f64::from_bits(16);
        //! let small = Vector::<5>::try_new([3.0 * tiny, 4.0 * tiny, 0.0, 0.0, 0.0])?;
        //! assert_eq!(small.norm()?, 5.0 * tiny);
        //! assert_eq!(small.norm_squared()?, 0.0); // The raw squares underflow.
        //! # Ok(())
        //! # }
        //! ```
        //!
        //! The large-vector assertion uses a tolerance for this fixture, not a certified
        //! error bound. The small vector shows why taking the square root of
        //! `norm_squared()` can lose a representable nonzero norm.
    }

    pub mod certified {
        //! Certified dot products and affine differences.
        //!
        //! `Vector::dot_with_errbound()` evaluates the same left-to-right FMA tree as
        //! `Vector::dot()` and returns its estimate together with a certified absolute
        //! roundoff bound. `Vector::dot_difference_with_errbound()` directly evaluates
        //!
        //! ```text
        //! Σᵢ axis[i] × (left[i] - right[i])
        //! ```
        //!
        //! as two FMAs per coordinate. It does not first round `left - right` into a new
        //! `Vector`, so the certificate covers the intended expression over the original
        //! stored binary64 coordinates.
        //!
        //! The opaque [`ScalarWithErrorBound`](crate::ScalarWithErrorBound) exposes the estimate, absolute error bound,
        //! and finite outward-rounded lower and upper bounds. Those endpoints support
        //! positive, negative, and caller-selected threshold proofs:
        //!
        //! # A certified dot-product sign
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! # fn main() -> Result<(), LaError> {
        //! let axis = Vector::<5>::try_new([2.0, -1.0, 3.0, 1.0, -2.0])?;
        //! let point = Vector::<5>::try_new([4.0, 1.0, 2.0, 3.0, 1.0])?;
        //! let positive = axis.dot_with_errbound(&point)?.and_then(|value| {
        //!     if value.lower_bound() > 0.0 {
        //!         Some(true)
        //!     } else if value.upper_bound() <= 0.0 {
        //!         Some(false)
        //!     } else {
        //!         None // An enclosure overlapping zero is inconclusive.
        //!     }
        //! });
        //! assert_eq!(positive, Some(true));
        //! # Ok(())
        //! # }
        //! ```
        //!
        //! # An affine threshold test
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! fn is_separated<const D: usize>(
        //!     axis: &Vector<D>,
        //!     left: &Vector<D>,
        //!     right: &Vector<D>,
        //!     threshold: f64,
        //! ) -> Result<Option<bool>, LaError> {
        //!     let Some(value) = axis.dot_difference_with_errbound(left, right)? else {
        //!         return Ok(None);
        //!     };
        //!     if value.lower_bound() > threshold {
        //!         Ok(Some(true))
        //!     } else if value.upper_bound() <= threshold {
        //!         Ok(Some(false))
        //!     } else {
        //!         Ok(None)
        //!     }
        //! }
        //!
        //! # fn main() -> Result<(), LaError> {
        //! let axis = Vector::<2>::try_new([2.0, -1.0])?;
        //! let left = Vector::<2>::try_new([4.0, 1.0])?;
        //! let right = Vector::<2>::try_new([1.0, 3.0])?;
        //! assert_eq!(is_separated(&axis, &left, &right, 1.0)?, Some(true));
        //! # Ok(())
        //! # }
        //! ```
        //!
        //! An interval that overlaps the threshold is inconclusive, not equal. Likewise,
        //! `Ok(None)` means gradual underflow or proof-only range exhaustion prevented a
        //! certificate. A filtered-exact caller should rebuild the same dot or affine
        //! expression in `BigRational` (available through the `exact` feature) or another
        //! exact backend. A `LaError::NonFinite` instead reports that the specified FMA
        //! estimate itself overflowed. These certified bounds describe roundoff in a fixed
        //! arithmetic tree; they are distinct from user-selected numerical tolerances.
    }

    pub mod adaptive {
        //! Adaptive determinant filtering with certified bounds.
        //!
        //! [`det_direct_with_errbound()`](crate::Matrix::det_direct_with_errbound) returns a closed-form determinant together with
        //! the conservative absolute error bound used by the fast filter, computed from
        //! one call that evaluates the determinant once and computes its matching bound.
        //! It returns `None` when a D ≤ 4 computation may be affected by gradual
        //! underflow, as well as for unsupported D ≥ 5 dimensions.
        //! It returns `LaError::NonFinite` if the determinant or bound computation
        //! overflows to NaN or infinity.
        //! This method does NOT require the `exact` feature — it uses pure f64 arithmetic
        //! and is available by default. Use [`det_errbound()`](crate::Matrix::det_errbound) when only the bound is needed.
        //! The paired API enables custom adaptive-precision logic for geometric predicates:
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! # fn main() -> Result<(), LaError> {
        //! let matrix = Matrix::<3>::identity();
        //! let sign = matrix.det_direct_with_errbound()?.and_then(|value| {
        //!     if value.determinant() > value.absolute_error_bound() {
        //!         Some(1)
        //!     } else if -value.determinant() > value.absolute_error_bound() {
        //!         Some(-1)
        //!     } else {
        //!         None // The bound cannot establish a sign.
        //!     }
        //! });
        //! assert_eq!(sign, Some(1));
        //! # Ok(())
        //! # }
        //! ```
        //!
        //! With the `exact` feature, `Matrix::det_sign_exact()`
        //! already handles filtering and exact fallback. The
        //! [custom adaptive example](https://docs.rs/la-stack/latest/la_stack/guide/exact/index.html#adaptive-determinant-filtering)
        //! shows positive, singular, and overflowing filter cases. It requires `exact`.
        //!
        //! The error coefficients (`ERR_COEFF_2`, `ERR_COEFF_3`, `ERR_COEFF_4`) are
        //! conservative, dimension-specific constants, not caller-tunable tolerances. The
        //! [mathematical basis](https://github.com/acgetchell/la-stack/blob/v0.4.5/docs/mathematical_basis.md#determinants-and-certified-sign-filtering)
        //! documents the bound and states its range preconditions. The constants are explicit
        //! crate-root exports for advanced users who want to compose the same bound:
        //! `use la_stack::{ERR_COEFF_2, ERR_COEFF_3, ERR_COEFF_4};`. They intentionally stay
        //! out of the common prelude.
    }

    #[cfg(feature = "exact")]
    pub mod exact {
        //! Exact arithmetic over stored binary64 and rational inputs.
        //!
        //! The default build has **zero runtime dependencies**. Enable the optional
        //! `exact` Cargo feature to add exact arithmetic methods using arbitrary-precision
        //! rationals (this pulls in `num-bigint`, `num-rational`, and `num-traits` for
        //! `BigRational`):
        //!
        //! See the [crate-level installation instructions](crate) for Cargo configuration.
        //!
        //! The feature exposes two deliberate input domains:
        //!
        //! - `Matrix<D>` / `Vector<D>` store finite binary64 inputs. Their exact methods
        //!   treat each stored bit pattern as its exact rational value, so the determinant
        //!   or solve stage introduces no further roundoff. They cannot recover information
        //!   already lost before construction.
        //! - `RationalMatrix<D>` / `RationalVector<D>` accept coefficients already
        //!   assembled as `BigRational`. They preserve derived differences, squared norms,
        //!   affine coefficients, and other rational expressions without an intermediate
        //!   `f64` conversion.
        //!
        //! **Determinants:**
        //!
        //! - **`det_exact()`** — returns the exact determinant as a `BigRational`
        //! - **`det_exact_f64()`** — returns the exact determinant as `f64` only when
        //!   it is exactly representable (or `LaError::Unrepresentable` otherwise)
        //! - **`det_exact_rounded_f64()`** — returns the exact determinant rounded to a
        //!   finite `f64` using IEEE 754 round-to-nearest, ties-to-even
        //! - **`det_sign_exact()`** — infallibly returns the provably correct
        //!   `DeterminantSign` variant (`Negative`, `Zero`, or `Positive`)
        //!
        //! **Linear system solve:**
        //!
        //! - **`solve_exact(b)`** — solves `Ax = b` exactly, returning a
        //!   `RationalVector<D>`
        //! - **`solve_exact_f64(b)`** — solves `Ax = b` exactly, returning `Vector<D>` only when
        //!   every component is exactly representable as `f64`
        //! - **`solve_exact_rounded_f64(b)`** — solves `Ax = b` exactly, returning each
        //!   component rounded to finite `f64` using IEEE 754 round-to-nearest,
        //!   ties-to-even
        //! - **`ExactF64Conversion`** — converts an existing exact determinant or solution
        //!   under the strict or rounded contract without repeating exact elimination
        //!
        //! **Already-exact rational input:**
        //!
        //! - **`RationalMatrix::det_sign()`** — returns the exact sign without constructing
        //!   a rational determinant
        //! - **`RationalMatrix::det()`** — returns the exact `BigRational` determinant
        //! - **`RationalMatrix::solve(&rhs)`** — returns a `RationalVector<D>` exact
        //!   solution
        //! - **`try_with_rational_matrix!`** — dispatches a runtime-selected dimension
        //!   through D=8 to a const-generic rational matrix on stable Rust
        //!
        //! The `Matrix::det_exact*` value and conversion methods return
        //! `LaError::DeterminantScaleOverflow` if their aggregate power-of-two scaling
        //! exceeds the internal exponent representation. `RationalMatrix::det()` is
        //! infallible because it clears rational row denominators without an exponent-scale
        //! conversion. The exact solve methods for both input domains return
        //! `LaError::Singular` with `SingularityReason::Exact` when the stored matrix is
        //! exactly singular.
        //!
        //! For exact-to-f64 output, strict conversions use
        //! `UnrepresentableReason::RequiresRounding` when explicit rounding can produce a
        //! finite value and `UnrepresentableReason::NotFinite` otherwise. Rounded
        //! conversions opt into nearest-even rounding but still report `NotFinite` when no
        //! finite `f64` exists.
        //!
        //! # Preserving rational inputs
        //!
        //! The following 5×5 system has exact determinant 2^-60. Its exact rational inputs
        //! therefore produce a unique solution through the general Bareiss path. Supplying
        //! the same coefficients as `f64` inputs loses the `2^-60` perturbation at `1.0`,
        //! making the leading rows identical and the binary64 system singular.
        //!
        //! ```rust
        //! use core::assert_matches;
        //!
        //! use la_stack::prelude::*;
        //!
        //! fn main() -> Result<(), LaError> {
        //!     // This is far below one binary64 ULP at 1.0, so 1.0 + 2^-60 rounds to 1.0.
        //!     let epsilon = BigRational::new(1.into(), (1_u64 << 60).into());
        //!     let one = BigRational::from_integer(1.into());
        //!     let zero = BigRational::from_integer(0.into());
        //!
        //!     // The leading block is [[1, 1], [1, 1 + 2^-60]]. The remaining diagonal
        //!     // extends the example to D=5, where the general Bareiss path is used.
        //!     let matrix = RationalMatrix::<5>::try_from_fn(|row, col| match (row, col) {
        //!         (0, 0 | 1) | (1, 0) => one.clone(),
        //!         (1, 1) => &one + &epsilon,
        //!         _ if row == col => one.clone(),
        //!         _ => zero.clone(),
        //!     })?;
        //!     assert_eq!(matrix.det_sign(), DeterminantSign::Positive);
        //!     assert_eq!(matrix.det(), epsilon);
        //!
        //!     let rhs = RationalVector::try_new([
        //!         zero,
        //!         -&epsilon,
        //!         BigRational::from_integer(2.into()),
        //!         BigRational::from_integer(3.into()),
        //!         BigRational::from_integer(4.into()),
        //!     ])?;
        //!     let exact_solution = matrix.solve(&rhs)?;
        //!     assert_eq!(
        //!         exact_solution.as_array(),
        //!         &[
        //!             BigRational::from_integer(1.into()),
        //!             BigRational::from_integer((-1).into()),
        //!             BigRational::from_integer(2.into()),
        //!             BigRational::from_integer(3.into()),
        //!             BigRational::from_integer(4.into()),
        //!         ]
        //!     );
        //!
        //!     // Supplying the same coefficients as f64 inputs destroys the perturbation
        //!     // and makes the matrix singular, even though the exact solution is integral.
        //!     let epsilon_f64 = epsilon.try_to_f64()?;
        //!     assert_eq!((1.0 + epsilon_f64).to_bits(), 1.0_f64.to_bits());
        //!     let f64_matrix = Matrix::<5>::try_from_rows([
        //!         [1.0, 1.0, 0.0, 0.0, 0.0],
        //!         [1.0, 1.0 + epsilon_f64, 0.0, 0.0, 0.0],
        //!         [0.0, 0.0, 1.0, 0.0, 0.0],
        //!         [0.0, 0.0, 0.0, 1.0, 0.0],
        //!         [0.0, 0.0, 0.0, 0.0, 1.0],
        //!     ])?;
        //!     let f64_rhs = Vector::<5>::try_new([0.0, -epsilon_f64, 2.0, 3.0, 4.0])?;
        //!     let f64_solve = f64_matrix
        //!         .lu(DEFAULT_SINGULAR_TOL)
        //!         .and_then(|lu| lu.solve(f64_rhs));
        //!     assert_matches!(
        //!         f64_solve,
        //!         Err(LaError::Singular { .. })
        //!     );
        //!     Ok(())
        //! }
        //! ```
        //!
        //! # Stored binary64 inputs and output conversion
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! fn main() -> Result<(), LaError> {
        //!     // Exact determinant
        //!     let m = Matrix::<3>::try_from_rows([
        //!         [1.0, 2.0, 3.0],
        //!         [4.0, 5.0, 6.0],
        //!         [7.0, 8.0, 9.0],
        //!     ])?;
        //!     assert_eq!(m.det_sign_exact(), DeterminantSign::Zero); // exactly singular
        //!
        //!     let det = m.det_exact()?;
        //!     assert_eq!(det, BigRational::from_integer(0.into())); // exact zero
        //!     let det_f64 = det.try_to_f64()?;
        //!     assert_eq!(det_f64, 0.0);
        //!
        //!     // If strict exact-to-f64 conversion would require rounding, opt in
        //!     // explicitly with the rounded API.
        //!     let inexact = Matrix::<2>::try_from_rows([
        //!         [1.0 + f64::EPSILON, 0.0],
        //!         [0.0, 1.0 - f64::EPSILON],
        //!     ])?;
        //!     let exact_det = inexact.det_exact()?;
        //!     let rounded_det = match exact_det.try_to_f64() {
        //!         Ok(det) => det,
        //!         Err(err) if err.requires_rounding() => exact_det.to_rounded_f64()?,
        //!         Err(err) => return Err(err),
        //!     };
        //!     assert_eq!(rounded_det.to_bits(), 1.0f64.to_bits());
        //!
        //!     // If the exact determinant cannot fit in f64, keep the BigRational value.
        //!     let big = f64::MAX / 2.0;
        //!     let huge = Matrix::<3>::try_from_rows([
        //!         [0.0, 0.0, 1.0],
        //!         [big, 0.0, 1.0],
        //!         [0.0, big, 1.0],
        //!     ])?;
        //!     let huge_det = huge.det_exact()?;
        //!     assert_eq!(
        //!         huge_det
        //!             .try_to_f64()
        //!             .err()
        //!             .and_then(|err| err.unrepresentable_reason()),
        //!         Some(UnrepresentableReason::NotFinite)
        //!     );
        //!     println!("exact determinant = {huge_det}");
        //!
        //!     // Exact linear system solve
        //!     let a = Matrix::<2>::try_from_rows([[1.0, 2.0], [3.0, 4.0]])?;
        //!     let b = Vector::<2>::try_new([5.0, 11.0])?;
        //!     let exact_x = a.solve_exact(b)?;
        //!     let x = exact_x.try_to_f64()?.into_array();
        //!     assert!((x[0] - 1.0).abs() <= f64::EPSILON);
        //!     assert!((x[1] - 2.0).abs() <= f64::EPSILON);
        //!
        //!     Ok(())
        //! }
        //! ```
        //!
        //! With the `exact` feature enabled, `RationalMatrix`, `RationalVector`,
        //! `DeterminantSign`, `ExactF64Conversion`, `BigInt`, and `BigRational` are
        //! re-exported from the crate root and prelude,
        //! alongside the most commonly needed `num-traits` items (`FromPrimitive`,
        //! `ToPrimitive`, `Signed`). This lets consumers construct exact values
        //! (`BigRational::from_f64`, `from_i64`), query sign (`is_positive` /
        //! `is_negative`), and convert back to `f64` (`try_to_f64`, `to_rounded_f64`, or
        //! the raw `to_f64`) with a single
        //! `use la_stack::prelude::*;` — no need to add `num-bigint`, `num-rational`,
        //! or `num-traits` to their own `Cargo.toml`. Use
        //! `DeterminantSign::as_i8()` only when numeric −1/0/+1 interoperability is
        //! required.
        //!
        //! For `det_sign_exact()`, D ≤ 4 matrices first use a fast f64 filter
        //! (error-bounded [`det_direct_with_errbound()`](crate::Matrix::det_direct_with_errbound)) when its rounded intermediates stay in the normal
        //! range or are exact structural zeros. An inconclusive filter falls back to the
        //! same direct determinant expansion in `BigInt`. D ≥ 5 skips the closed-form
        //! filter and uses fraction-free Bareiss elimination in `BigInt`.
        //! Because `Matrix` stores only finite entries, arithmetic range failures in the
        //! filter are inconclusive rather than errors and the exact fallback is total.
        //!
        //! # A five-dimensional rational solve
        //!
        //! ```rust
        //! use core::assert_matches;
        //!
        //! use la_stack::prelude::*;
        //!
        //! # fn main() -> Result<(), LaError> {
        //! // A tridiagonal exact matrix with determinant 6.
        //! let matrix = RationalMatrix::<5>::try_from_fn(|row, col| {
        //!     BigRational::from_integer(if row == col {
        //!         2.into()
        //!     } else if row.abs_diff(col) == 1 {
        //!         1.into()
        //!     } else {
        //!         0.into()
        //!     })
        //! })?;
        //! let numerators = [4, 8, 12, 16, 14];
        //! let rhs = RationalVector::try_from_fn(|row| {
        //!     BigRational::new(numerators[row].into(), 3.into())
        //! })?;
        //! let solution = matrix.solve(&rhs)?;
        //! let expected = [1, 2, 3, 4, 5].map(|n| BigRational::new(n.into(), 3.into()));
        //! assert_eq!(solution.as_array(), &expected);
        //!
        //! // Keep the exact solution until the caller explicitly opts into rounding.
        //! assert_matches!(
        //!     solution.try_to_f64(),
        //!     Err(LaError::Unrepresentable {
        //!         index: Some(0),
        //!         reason: UnrepresentableReason::RequiresRounding,
        //!         ..
        //!     })
        //! );
        //! let rounded = solution.to_rounded_f64()?;
        //! assert_eq!(rounded.as_array(), &[1.0 / 3.0, 2.0 / 3.0, 1.0, 4.0 / 3.0, 5.0 / 3.0]);
        //! # Ok(())
        //! # }
        //! ```
        //!
        //! # Rational dimension dispatch
        //!
        //! [`try_with_rational_matrix!`](crate::try_with_rational_matrix) selects a
        //! concrete `RationalMatrix<N>` for dimensions 0 through
        //! [`MAX_RATIONAL_MATRIX_DISPATCH_DIM`](crate::MAX_RATIONAL_MATRIX_DISPATCH_DIM)
        //! (8). Larger dimensions return [`LaError::UnsupportedDimension`](crate::LaError::UnsupportedDimension),
        //! converted through `From<LaError>` into the closure's declared error type.
        //! The macro preserves the const-generic representation.
        //!
        //! Rational constructors include `try_from_rows` / `try_new` and
        //! `try_from_fn`; `as_rows` / `as_array` and `get` borrow their stored
        //! values, while `into_rows` / `into_array` return the owned arrays.
        //!
        //! # Adaptive determinant filtering
        //!
        //! This example requires `exact` and illustrates a custom filter with exact
        //! fallback. Use [`Matrix::det_sign_exact`](crate::Matrix::det_sign_exact) directly
        //! when no custom filtering policy is needed.
        //!
        //! ```rust
        //! use la_stack::prelude::*;
        //!
        //! fn adaptive_det_sign<const D: usize>(
        //!     matrix: &Matrix<D>,
        //! ) -> DeterminantSign {
        //!     if let Ok(Some(estimate)) = matrix.det_direct_with_errbound() {
        //!         if estimate.determinant().abs() > estimate.absolute_error_bound() {
        //!             return if estimate.determinant() > 0.0 {
        //!                 DeterminantSign::Positive
        //!             } else {
        //!                 DeterminantSign::Negative
        //!             };
        //!         }
        //!     }
        //!
        //!     matrix.det_sign_exact()
        //! }
        //!
        //! fn main() -> Result<(), LaError> {
        //!     let identity = Matrix::<3>::identity();
        //!     assert_eq!(
        //!         adaptive_det_sign(&identity),
        //!         DeterminantSign::Positive
        //!     );
        //!
        //!     // A zero determinant cannot pass the f64 sign filter, so this exercises
        //!     // the exact fallback.
        //!     let singular = Matrix::<3>::try_from_rows([
        //!         [1.0, 2.0, 3.0],
        //!         [4.0, 5.0, 6.0],
        //!         [7.0, 8.0, 9.0],
        //!     ])?;
        //!     assert_eq!(adaptive_det_sign(&singular), DeterminantSign::Zero);
        //!
        //!     // The f64 filter overflows for this finite matrix, but the exact fallback
        //!     // still resolves its positive determinant sign.
        //!     let big = f64::MAX / 2.0;
        //!     let overflowing = Matrix::<3>::try_from_rows([
        //!         [0.0, 0.0, 1.0],
        //!         [big, 0.0, 1.0],
        //!         [0.0, big, 1.0],
        //!     ])?;
        //!     assert_eq!(
        //!         adaptive_det_sign(&overflowing),
        //!         DeterminantSign::Positive
        //!     );
        //!
        //!     Ok(())
        //! }
        //! ```
    }
}
mod angle;
mod error;
#[cfg(feature = "exact")]
mod exact;
mod gram;
mod interval;
mod ldlt;
mod lu;
mod matrix;
mod norm;
#[cfg(feature = "exact")]
mod rational;
mod rounding;
mod scaled_product;
mod tolerance;
mod vector;

#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
pub use exact::{DeterminantSign, ExactF64Conversion};
#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
pub use num_bigint::BigInt;
#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
pub use num_rational::BigRational;
#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
pub use num_traits::{FromPrimitive, Signed, ToPrimitive};
#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
pub use rational::{RationalMatrix, RationalVector};

// ---------------------------------------------------------------------------
// Error-bound constants for `Matrix::det_direct_with_errbound()` and
// `Matrix::det_errbound()`.
//
// For `D ∈ {2, 3, 4}`, `Matrix::det_direct()` evaluates the Leibniz expansion
// of the determinant as a tree of f64 multiplies and fused multiply-adds
// (FMAs).  When every rounded intermediate is normal or an exact structural
// zero, Shewchuk's error-analysis methodology (REFERENCES.md [8]) bounds the
// absolute error of that computation by
//
//     |det_direct(A) - det_exact(A)|  ≤  ERR_COEFF_D · p(|A|)
//
// where `p(|A|)` is the **absolute Leibniz sum**
//
//     p(|A|) = Σ_σ ∏ᵢ |A[i, σ(i)]|,
//
// i.e. exactly the combinatorial matrix permanent `perm(|A|)`. The
// implementation evaluates the corresponding fixed-size expansion in f64, so
// the computed `permanent` value used by the bound may itself be rounded even
// though the mathematical quantity above is exact.
//
// The longest rounding paths in the determinant and permanent have lengths
// k = 2, 5, and 9. With EPS = 2^-52, gamma_k = k*EPS / (1 - k*EPS) bounds
// their accumulated relative perturbations. Each exactly representable
// coefficient satisfies c >= gamma_k / ((1 - EPS)*(1 - gamma_k)), including
// possible downward rounding of both the permanent and the final product.
// See docs/mathematical_basis.md, "Derivation of the returned determinant
// bound", for the full argument and the underflow assumptions.
//
// These constants are NOT feature-gated — they rely only on f64 arithmetic
// and are useful for adaptive-precision logic even without the `exact`
// feature. Most callers should prefer `Matrix::det_direct_with_errbound()`
// when they need the approximation and bound together, or
// `Matrix::det_errbound()` when they need only the bound. Those methods apply
// these constants to the actual matrix; the raw constants are
// exposed for advanced use cases (composing the bound with a pre-reduced
// permanent, rolling a custom adaptive filter, etc.).  See
// `Matrix::det_sign_exact()` (behind the `exact` feature) for the
// reference adaptive-filter that consumes these internally.
// ---------------------------------------------------------------------------

const EPS: f64 = f64::EPSILON; // 2^-52

/// Absolute error coefficient for [`Matrix::<2>::det_direct`](crate::Matrix::det_direct).
///
/// This constant is not a caller-tuned tolerance. It is the dimension-specific
/// multiplier that turns the matrix's absolute Leibniz sum into a conservative
/// bound on floating-point roundoff in the closed-form 2×2 determinant formula.
///
/// For a 2×2 matrix `A = [[a, b], [c, d]]` whose closed-form determinant
/// intermediates do not undergo gradual underflow,
///
/// ```text
/// |A.det_direct() - det_exact(A)|  ≤  ERR_COEFF_2 · (|a·d| + |b·c|)
/// ```
///
/// `det_direct` evaluates `a·d - b·c` as one multiply followed by one FMA
/// (2 rounding events on the longest path). The permanent also has a
/// two-event path. The coefficient covers both trees and the final rounded
/// multiplication; see the
/// [returned-bound derivation](https://github.com/acgetchell/la-stack/blob/main/docs/mathematical_basis.md#derivation-of-the-returned-determinant-bound).
/// The analysis follows Shewchuk's framework and the binary64 arithmetic
/// model; see `REFERENCES.md` \[8-11\].
///
/// Prefer
/// [`Matrix::det_direct_with_errbound`](crate::Matrix::det_direct_with_errbound)
/// unless you need only the bound or already have the absolute-Leibniz sum;
/// see
/// `Matrix::det_sign_exact` (under the `exact` feature) for the reference
/// adaptive-precision filter.
///
/// # Example
/// ```
/// use la_stack::{prelude::*, ERR_COEFF_2};
///
/// # fn main() -> Result<(), LaError> {
/// let m = Matrix::<2>::try_from_rows([[1.0, 2.0], [3.0, 4.0]])?;
/// let det = m.det_direct()?;
/// assert_eq!(det, Some(-2.0));
/// // Compute the bound from the raw constant for illustration; most
/// // callers would match on `m.det_errbound()?` instead.
/// let p = (1.0_f64 * 4.0).abs() + (2.0_f64 * 3.0).abs();
/// let bound = ERR_COEFF_2 * p;
/// // The f64 sign is provably correct without exact arithmetic.
/// assert_eq!(det.map(|value| value.abs() > bound), Some(true));
/// # Ok(())
/// # }
/// ```
pub const ERR_COEFF_2: f64 = 3.0 * EPS + 16.0 * EPS * EPS;

/// Absolute error coefficient for [`Matrix::<3>::det_direct`](crate::Matrix::det_direct).
///
/// This constant is not a caller-tuned tolerance. It is the dimension-specific
/// multiplier that turns the matrix's absolute Leibniz sum into a conservative
/// bound on floating-point roundoff in the closed-form 3×3 determinant formula.
///
/// For a 3×3 matrix `A` whose closed-form determinant intermediates do not
/// undergo gradual underflow,
///
/// ```text
/// |A.det_direct() - det_exact(A)|  ≤  ERR_COEFF_3 · p(|A|)
/// ```
///
/// where `p(|A|)` is the absolute Leibniz sum (the same cofactor
/// expansion as `det_direct` but with `|·|` at every leaf).
/// `det_direct` for D=3 uses three 2×2 FMA minors combined by a nested
/// FMA. The determinant and permanent each have at most five rounding events
/// per monomial; `8·EPS + 64·EPS²` also covers rounding the permanent and final
/// bound product. See [`ERR_COEFF_2`] for the derivation link and
/// `REFERENCES.md` \[8-11\] for the analysis framework.
///
/// Prefer
/// [`Matrix::det_direct_with_errbound`](crate::Matrix::det_direct_with_errbound)
/// over this constant for typical use; see [`ERR_COEFF_2`] for a worked
/// example.
pub const ERR_COEFF_3: f64 = 8.0 * EPS + 64.0 * EPS * EPS;

/// Absolute error coefficient for [`Matrix::<4>::det_direct`](crate::Matrix::det_direct).
///
/// This constant is not a caller-tuned tolerance. It is the dimension-specific
/// multiplier that turns the matrix's absolute Leibniz sum into a conservative
/// bound on floating-point roundoff in the closed-form 4×4 determinant formula.
///
/// For a 4×4 matrix `A` whose closed-form determinant intermediates do not
/// undergo gradual underflow,
///
/// ```text
/// |A.det_direct() - det_exact(A)|  ≤  ERR_COEFF_4 · p(|A|)
/// ```
///
/// where `p(|A|)` is the absolute Leibniz sum. `det_direct` for D=4
/// evaluates four nested 3×3 cofactors, sharing their six 2×2 minors when
/// every coefficient in the first two rows is non-zero, and reduces them with
/// an FMA row combination. Dense and sparse trees each have at most nine
/// rounding events per monomial, as does the permanent tree. The coefficient
/// `12·EPS + 128·EPS²` also covers rounding the permanent and final bound
/// product. See [`ERR_COEFF_2`] for the derivation link and `REFERENCES.md`
/// \[8-11\] for the analysis framework.
///
/// Prefer
/// [`Matrix::det_direct_with_errbound`](crate::Matrix::det_direct_with_errbound)
/// over this constant for typical use; see [`ERR_COEFF_2`] for a worked
/// example.
pub const ERR_COEFF_4: f64 = 12.0 * EPS + 128.0 * EPS * EPS;

/// Largest dimension supported by [`try_with_stack_matrix!`].
///
/// The crate can represent `Matrix<D>` for any compile-time `D`, but runtime
/// dispatch must enumerate a finite set of concrete stack types.  Dimensions
/// `0..=7` cover downstream geometric predicate matrices while keeping the
/// dispatch surface explicit.
pub const MAX_STACK_MATRIX_DISPATCH_DIM: usize = 7;

/// Largest dimension supported by [`try_with_rational_matrix!`].
///
/// This bound covers exact downstream geometric systems through dimension 8
/// while keeping runtime-to-const dispatch explicit and available on stable
/// Rust.
#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
pub const MAX_RATIONAL_MATRIX_DISPATCH_DIM: usize = 8;

pub use angle::VectorAngle;
pub use error::{
    ArithmeticOperation, FactorizationKind, IntervalBound, IntervalOperand, InvalidToleranceReason,
    LaError, NonFiniteLocation, NonFiniteOrigin, PositiveSemidefiniteViolation, SingularityReason,
    UnrepresentableReason, VectorOperand,
};
pub use gram::gram_matrix;
pub use interval::{Interval, IntervalDeterminantSign, IntervalMatrix, MAX_INTERVAL_MATRIX_DIM};
pub use ldlt::Ldlt;
pub use lu::Lu;
pub use matrix::{DeterminantWithErrorBound, Matrix};
pub use tolerance::{DEFAULT_SINGULAR_TOL, Tolerance};
pub use vector::{ScalarWithErrorBound, Vector};

/// Fallibly dispatch a runtime dimension to a concrete stack-allocated matrix.
///
/// The macro creates a zero matrix with type `Matrix<N>` for the selected
/// runtime dimension `N`, then evaluates the supplied closure body.  Supported
/// runtime dimensions run from `0` through [`MAX_STACK_MATRIX_DISPATCH_DIM`].
/// The body may mutate or consume captured values. It is not evaluated for
/// unsupported dimensions.
/// Unsupported dimensions return
/// `Err(LaError::UnsupportedDimension { requested, max })` converted with
/// `From<LaError>`, so downstream crates can use their own public error type.
///
/// # Errors
/// Returns [`LaError::UnsupportedDimension`] (converted through `From<LaError>`)
/// when the requested runtime dimension is greater than
/// [`MAX_STACK_MATRIX_DISPATCH_DIM`].  The closure body may return any other
/// error representable by its declared `Result` type.
///
/// # Examples
/// ```
/// use la_stack::prelude::*;
///
/// # fn main() -> Result<(), LaError> {
/// let requested = 2usize;
/// let det = try_with_stack_matrix!(requested, |mut m| -> Result<f64, LaError> {
///     m.set(0, 0, 1.0)?;
///     m.set(1, 1, 1.0)?;
///     m.det()
/// })?;
///
/// assert_eq!(det, 1.0);
/// # Ok(())
/// # }
/// ```
#[macro_export]
macro_rules! try_with_stack_matrix {
    ($dim:expr, |$matrix:ident| -> $ret:ty $body:block $(,)?) => {{
        let __la_stack_requested_dim: usize = $dim;
        match __la_stack_requested_dim {
            0 => $crate::try_with_stack_matrix!(@arm 0, $matrix, $ret, $body),
            1 => $crate::try_with_stack_matrix!(@arm 1, $matrix, $ret, $body),
            2 => $crate::try_with_stack_matrix!(@arm 2, $matrix, $ret, $body),
            3 => $crate::try_with_stack_matrix!(@arm 3, $matrix, $ret, $body),
            4 => $crate::try_with_stack_matrix!(@arm 4, $matrix, $ret, $body),
            5 => $crate::try_with_stack_matrix!(@arm 5, $matrix, $ret, $body),
            6 => $crate::try_with_stack_matrix!(@arm 6, $matrix, $ret, $body),
            7 => $crate::try_with_stack_matrix!(@arm 7, $matrix, $ret, $body),
            requested => Err(::core::convert::From::from(
                $crate::LaError::unsupported_dimension(
                    requested,
                    $crate::MAX_STACK_MATRIX_DISPATCH_DIM,
                ),
            )),
        }
    }};
    ($dim:expr, |mut $matrix:ident| -> $ret:ty $body:block $(,)?) => {{
        let __la_stack_requested_dim: usize = $dim;
        match __la_stack_requested_dim {
            0 => $crate::try_with_stack_matrix!(@arm_mut 0, $matrix, $ret, $body),
            1 => $crate::try_with_stack_matrix!(@arm_mut 1, $matrix, $ret, $body),
            2 => $crate::try_with_stack_matrix!(@arm_mut 2, $matrix, $ret, $body),
            3 => $crate::try_with_stack_matrix!(@arm_mut 3, $matrix, $ret, $body),
            4 => $crate::try_with_stack_matrix!(@arm_mut 4, $matrix, $ret, $body),
            5 => $crate::try_with_stack_matrix!(@arm_mut 5, $matrix, $ret, $body),
            6 => $crate::try_with_stack_matrix!(@arm_mut 6, $matrix, $ret, $body),
            7 => $crate::try_with_stack_matrix!(@arm_mut 7, $matrix, $ret, $body),
            requested => Err(::core::convert::From::from(
                $crate::LaError::unsupported_dimension(
                    requested,
                    $crate::MAX_STACK_MATRIX_DISPATCH_DIM,
                ),
            )),
        }
    }};
    (@arm $d:literal, $matrix:ident, $ret:ty, $body:block) => {{
        let mut __la_stack_body = |$matrix: $crate::Matrix<$d>| -> $ret { $body };
        __la_stack_body($crate::Matrix::<$d>::zero())
    }};
    (@arm_mut $d:literal, $matrix:ident, $ret:ty, $body:block) => {{
        let mut __la_stack_body = |mut $matrix: $crate::Matrix<$d>| -> $ret { $body };
        __la_stack_body($crate::Matrix::<$d>::zero())
    }};
}

/// Fallibly dispatch a runtime dimension to a concrete interval matrix.
///
/// The macro creates a zero [`IntervalMatrix`] with the selected const-generic
/// dimension, then evaluates the closure body. Supported dimensions run from
/// `0` through [`MAX_INTERVAL_MATRIX_DIM`]. Unsupported dimensions return
/// [`LaError::UnsupportedDimension`] converted through `From<LaError>`.
/// The body may mutate or consume captured values. It is not evaluated for
/// unsupported dimensions.
///
/// # Errors
/// Returns [`LaError::UnsupportedDimension`] (converted through
/// `From<LaError>`) when the requested dimension is greater than
/// [`MAX_INTERVAL_MATRIX_DIM`]. The closure body may return any other error
/// representable by its declared `Result` type.
///
/// # Examples
/// ```
/// use la_stack::prelude::*;
///
/// # fn main() -> Result<(), LaError> {
/// let requested = 3usize;
/// let sign = try_with_interval_matrix!(requested, |mut matrix| -> Result<
///     IntervalDeterminantSign,
///     LaError,
/// > {
///     for index in 0..requested {
///         matrix.set(index, index, Interval::ONE)?;
///     }
///     matrix.det_sign()
/// })?;
/// assert_eq!(sign, IntervalDeterminantSign::Positive);
/// # Ok(())
/// # }
/// ```
#[macro_export]
macro_rules! try_with_interval_matrix {
    ($dim:expr, |$matrix:ident| -> $ret:ty $body:block $(,)?) => {{
        let __la_stack_requested_dim: usize = $dim;
        match __la_stack_requested_dim {
            0 => $crate::try_with_interval_matrix!(@arm 0, $matrix, $ret, $body),
            1 => $crate::try_with_interval_matrix!(@arm 1, $matrix, $ret, $body),
            2 => $crate::try_with_interval_matrix!(@arm 2, $matrix, $ret, $body),
            3 => $crate::try_with_interval_matrix!(@arm 3, $matrix, $ret, $body),
            4 => $crate::try_with_interval_matrix!(@arm 4, $matrix, $ret, $body),
            5 => $crate::try_with_interval_matrix!(@arm 5, $matrix, $ret, $body),
            6 => $crate::try_with_interval_matrix!(@arm 6, $matrix, $ret, $body),
            7 => $crate::try_with_interval_matrix!(@arm 7, $matrix, $ret, $body),
            requested => Err(::core::convert::From::from(
                $crate::LaError::unsupported_dimension(
                    requested,
                    $crate::MAX_INTERVAL_MATRIX_DIM,
                ),
            )),
        }
    }};
    ($dim:expr, |mut $matrix:ident| -> $ret:ty $body:block $(,)?) => {{
        let __la_stack_requested_dim: usize = $dim;
        match __la_stack_requested_dim {
            0 => $crate::try_with_interval_matrix!(@arm_mut 0, $matrix, $ret, $body),
            1 => $crate::try_with_interval_matrix!(@arm_mut 1, $matrix, $ret, $body),
            2 => $crate::try_with_interval_matrix!(@arm_mut 2, $matrix, $ret, $body),
            3 => $crate::try_with_interval_matrix!(@arm_mut 3, $matrix, $ret, $body),
            4 => $crate::try_with_interval_matrix!(@arm_mut 4, $matrix, $ret, $body),
            5 => $crate::try_with_interval_matrix!(@arm_mut 5, $matrix, $ret, $body),
            6 => $crate::try_with_interval_matrix!(@arm_mut 6, $matrix, $ret, $body),
            7 => $crate::try_with_interval_matrix!(@arm_mut 7, $matrix, $ret, $body),
            requested => Err(::core::convert::From::from(
                $crate::LaError::unsupported_dimension(
                    requested,
                    $crate::MAX_INTERVAL_MATRIX_DIM,
                ),
            )),
        }
    }};
    (@arm $d:literal, $matrix:ident, $ret:ty, $body:block) => {{
        let mut __la_stack_body = |$matrix: $crate::IntervalMatrix<$d>| -> $ret { $body };
        __la_stack_body($crate::IntervalMatrix::<$d>::zero())
    }};
    (@arm_mut $d:literal, $matrix:ident, $ret:ty, $body:block) => {{
        let mut __la_stack_body = |mut $matrix: $crate::IntervalMatrix<$d>| -> $ret { $body };
        __la_stack_body($crate::IntervalMatrix::<$d>::zero())
    }};
}

/// Fallibly dispatch a runtime dimension to a concrete exact rational matrix.
///
/// The macro creates a zero [`RationalMatrix`] with the selected const-generic
/// dimension, then evaluates the supplied closure body. Dimensions `0..=8` are
/// supported on stable Rust. The closure may fill the matrix through
/// [`RationalMatrix::set`] or replace it with a value built by
/// [`RationalMatrix::try_from_fn`].
/// The body may mutate or consume captured values. It is not evaluated for
/// unsupported dimensions.
///
/// # Errors
/// Returns [`LaError::UnsupportedDimension`] (converted through
/// `From<LaError>`) when the requested dimension is greater than
/// [`MAX_RATIONAL_MATRIX_DISPATCH_DIM`]. The closure body may return any other
/// error representable by its declared `Result` type.
///
/// # Examples
/// ```
/// use la_stack::prelude::*;
///
/// # fn main() -> Result<(), LaError> {
/// let requested = 3usize;
/// let sign = try_with_rational_matrix!(requested, |mut matrix| -> Result<
///     DeterminantSign,
///     LaError,
/// > {
///     for index in 0..requested {
///         matrix.set(index, index, BigRational::from_integer(1.into()))?;
///     }
///     Ok(matrix.det_sign())
/// })?;
/// assert_eq!(sign, DeterminantSign::Positive);
/// # Ok(())
/// # }
/// ```
#[cfg(feature = "exact")]
#[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
#[macro_export]
macro_rules! try_with_rational_matrix {
    ($dim:expr, |$matrix:ident| -> $ret:ty $body:block $(,)?) => {{
        let __la_stack_requested_dim: usize = $dim;
        match __la_stack_requested_dim {
            0 => $crate::try_with_rational_matrix!(@arm 0, $matrix, $ret, $body),
            1 => $crate::try_with_rational_matrix!(@arm 1, $matrix, $ret, $body),
            2 => $crate::try_with_rational_matrix!(@arm 2, $matrix, $ret, $body),
            3 => $crate::try_with_rational_matrix!(@arm 3, $matrix, $ret, $body),
            4 => $crate::try_with_rational_matrix!(@arm 4, $matrix, $ret, $body),
            5 => $crate::try_with_rational_matrix!(@arm 5, $matrix, $ret, $body),
            6 => $crate::try_with_rational_matrix!(@arm 6, $matrix, $ret, $body),
            7 => $crate::try_with_rational_matrix!(@arm 7, $matrix, $ret, $body),
            8 => $crate::try_with_rational_matrix!(@arm 8, $matrix, $ret, $body),
            requested => Err(::core::convert::From::from(
                $crate::LaError::unsupported_dimension(
                    requested,
                    $crate::MAX_RATIONAL_MATRIX_DISPATCH_DIM,
                ),
            )),
        }
    }};
    ($dim:expr, |mut $matrix:ident| -> $ret:ty $body:block $(,)?) => {{
        let __la_stack_requested_dim: usize = $dim;
        match __la_stack_requested_dim {
            0 => $crate::try_with_rational_matrix!(@arm_mut 0, $matrix, $ret, $body),
            1 => $crate::try_with_rational_matrix!(@arm_mut 1, $matrix, $ret, $body),
            2 => $crate::try_with_rational_matrix!(@arm_mut 2, $matrix, $ret, $body),
            3 => $crate::try_with_rational_matrix!(@arm_mut 3, $matrix, $ret, $body),
            4 => $crate::try_with_rational_matrix!(@arm_mut 4, $matrix, $ret, $body),
            5 => $crate::try_with_rational_matrix!(@arm_mut 5, $matrix, $ret, $body),
            6 => $crate::try_with_rational_matrix!(@arm_mut 6, $matrix, $ret, $body),
            7 => $crate::try_with_rational_matrix!(@arm_mut 7, $matrix, $ret, $body),
            8 => $crate::try_with_rational_matrix!(@arm_mut 8, $matrix, $ret, $body),
            requested => Err(::core::convert::From::from(
                $crate::LaError::unsupported_dimension(
                    requested,
                    $crate::MAX_RATIONAL_MATRIX_DISPATCH_DIM,
                ),
            )),
        }
    }};
    (@arm $d:literal, $matrix:ident, $ret:ty, $body:block) => {{
        let mut __la_stack_body = |$matrix: $crate::RationalMatrix<$d>| -> $ret { $body };
        __la_stack_body($crate::RationalMatrix::<$d>::zero())
    }};
    (@arm_mut $d:literal, $matrix:ident, $ret:ty, $body:block) => {{
        let mut __la_stack_body = |mut $matrix: $crate::RationalMatrix<$d>| -> $ret { $body };
        __la_stack_body($crate::RationalMatrix::<$d>::zero())
    }};
}

/// Common imports for ergonomic usage.
///
/// This prelude re-exports the primary types and common constants: [`Matrix`],
/// [`DeterminantWithErrorBound`], [`Interval`], [`IntervalMatrix`],
/// [`IntervalDeterminantSign`], [`ScalarWithErrorBound`], [`Vector`], [`Lu`],
/// [`Ldlt`], [`Tolerance`],
/// and [`LaError`]. It also includes the [`VectorAngle`] extension trait for
/// unsigned angles between borrowed coordinate slices and [`gram_matrix`] for
/// constructing a symmetric matrix of pairwise vector inner products. Its typed
/// error categories include [`ArithmeticOperation`], [`FactorizationKind`],
/// [`IntervalBound`], [`IntervalOperand`], [`InvalidToleranceReason`],
/// [`NonFiniteLocation`], [`NonFiniteOrigin`], [`PositiveSemidefiniteViolation`],
/// [`SingularityReason`], [`UnrepresentableReason`], and [`VectorOperand`]. It also re-exports
/// [`DEFAULT_SINGULAR_TOL`],
/// [`MAX_STACK_MATRIX_DISPATCH_DIM`], [`MAX_INTERVAL_MATRIX_DIM`],
/// [`try_with_stack_matrix!`], and [`try_with_interval_matrix!`] for
/// runtime-to-const matrix dispatch. Advanced custom-filter code should import
/// [`ERR_COEFF_2`], [`ERR_COEFF_3`], and [`ERR_COEFF_4`] explicitly from the
/// crate root; those raw coefficients intentionally stay out of the prelude.
#[cfg_attr(feature = "exact", doc = "")]
#[cfg_attr(
    feature = "exact",
    doc = "When the `exact` feature is enabled, [`RationalMatrix`], [`RationalVector`],"
)]
#[cfg_attr(
    feature = "exact",
    doc = "[`DeterminantSign`], [`ExactF64Conversion`], [`BigInt`], and [`BigRational`]"
)]
#[cfg_attr(
    feature = "exact",
    doc = "are also re-exported, together with [`MAX_RATIONAL_MATRIX_DISPATCH_DIM`] and"
)]
#[cfg_attr(
    feature = "exact",
    doc = "[`try_with_rational_matrix!`] for runtime-to-const exact-matrix dispatch."
)]
#[cfg_attr(
    feature = "exact",
    doc = "[`ExactF64Conversion`] converts an already-computed exact determinant or solution"
)]
#[cfg_attr(
    feature = "exact",
    doc = "under either the strict or explicitly rounded binary64 contract, without repeating"
)]
#[cfg_attr(
    feature = "exact",
    doc = "exact elimination. The number types let callers construct expected exact values"
)]
#[cfg_attr(
    feature = "exact",
    doc = "without adding `num-bigint` / `num-rational` to their own dependencies. The most"
)]
#[cfg_attr(
    feature = "exact",
    doc = "commonly needed `num-traits` items are re-exported alongside them: [`FromPrimitive`]"
)]
#[cfg_attr(
    feature = "exact",
    doc = "for `BigRational::from_f64` / `from_i64`, [`ToPrimitive`] for"
)]
#[cfg_attr(
    feature = "exact",
    doc = "`BigRational::to_f64` / `to_i64`, and [`Signed`] for `is_positive` / `is_negative` /"
)]
#[cfg_attr(feature = "exact", doc = "`abs`.")]
pub mod prelude {
    pub use crate::{
        ArithmeticOperation, DEFAULT_SINGULAR_TOL, DeterminantWithErrorBound, FactorizationKind,
        Interval, IntervalBound, IntervalDeterminantSign, IntervalMatrix, IntervalOperand,
        InvalidToleranceReason, LaError, Ldlt, Lu, MAX_INTERVAL_MATRIX_DIM,
        MAX_STACK_MATRIX_DISPATCH_DIM, Matrix, NonFiniteLocation, NonFiniteOrigin,
        PositiveSemidefiniteViolation, ScalarWithErrorBound, SingularityReason, Tolerance,
        UnrepresentableReason, Vector, VectorAngle, VectorOperand, gram_matrix,
        try_with_interval_matrix, try_with_stack_matrix,
    };

    #[cfg(feature = "exact")]
    #[cfg_attr(docsrs, doc(cfg(feature = "exact")))]
    pub use crate::{
        BigInt, BigRational, DeterminantSign, ExactF64Conversion, FromPrimitive,
        MAX_RATIONAL_MATRIX_DISPATCH_DIM, RationalMatrix, RationalVector, Signed, ToPrimitive,
        try_with_rational_matrix,
    };
}

#[cfg(test)]
mod tests {
    use approx::assert_abs_diff_eq;
    use pastey::paste;

    use super::*;

    macro_rules! gen_stack_matrix_dispatch_tests {
        ($d:literal) => {
            paste! {
                #[test]
                fn [<try_with_stack_matrix_dispatches_ $d d>]() {
                    let requested = $d;
                    let got = try_with_stack_matrix!(requested, |mut m| -> Result<usize, LaError> {
                        if $d > 0 {
                            m.set($d - 1, $d - 1, f64::from($d))?;
                            assert_abs_diff_eq!(
                                m.try_get($d - 1, $d - 1)?,
                                f64::from($d),
                                epsilon = 0.0
                            );
                        }
                        Ok($d)
                    });

                    assert_eq!(got, Ok($d));
                }
            }
        };
    }

    gen_stack_matrix_dispatch_tests!(1);
    gen_stack_matrix_dispatch_tests!(2);
    gen_stack_matrix_dispatch_tests!(3);
    gen_stack_matrix_dispatch_tests!(4);
    gen_stack_matrix_dispatch_tests!(5);
    gen_stack_matrix_dispatch_tests!(6);
    gen_stack_matrix_dispatch_tests!(7);

    macro_rules! gen_interval_matrix_dispatch_tests {
        ($d:literal) => {
            paste! {
                #[test]
                fn [<try_with_interval_matrix_dispatches_ $d d>]() {
                    let requested = $d;
                    let got = try_with_interval_matrix!(
                        requested,
                        |mut matrix| -> Result<IntervalDeterminantSign, LaError> {
                            let mut index = 0;
                            while index < $d {
                                matrix.set(index, index, Interval::ONE)?;
                                index += 1;
                            }
                            matrix.det_sign()
                        },
                    );

                    assert_eq!(got, Ok(IntervalDeterminantSign::Positive));
                }
            }
        };
    }

    gen_interval_matrix_dispatch_tests!(1);
    gen_interval_matrix_dispatch_tests!(2);
    gen_interval_matrix_dispatch_tests!(3);
    gen_interval_matrix_dispatch_tests!(4);
    gen_interval_matrix_dispatch_tests!(5);
    gen_interval_matrix_dispatch_tests!(6);
    gen_interval_matrix_dispatch_tests!(7);

    #[cfg(feature = "exact")]
    macro_rules! gen_rational_matrix_dispatch_tests {
        ($d:literal) => {
            paste! {
                #[test]
                fn [<try_with_rational_matrix_dispatches_ $d d>]() {
                    let requested = $d;
                    let got = try_with_rational_matrix!(
                        requested,
                        |mut matrix| -> Result<DeterminantSign, LaError> {
                            let mut index = 0;
                            while index < $d {
                                matrix.set(
                                    index,
                                    index,
                                    BigRational::from_integer(BigInt::from(1)),
                                )?;
                                index += 1;
                            }
                            Ok(matrix.det_sign())
                        },
                    );

                    assert_eq!(got, Ok(DeterminantSign::Positive));
                }
            }
        };
    }

    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(1);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(2);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(3);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(4);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(5);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(6);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(7);
    #[cfg(feature = "exact")]
    gen_rational_matrix_dispatch_tests!(8);

    #[cfg(feature = "exact")]
    #[test]
    fn try_with_rational_matrix_dispatches_zero_dimension() {
        let got = try_with_rational_matrix!(0usize, |matrix| -> Result<DeterminantSign, LaError> {
            Ok(matrix.det_sign())
        });

        assert_eq!(got, Ok(DeterminantSign::Positive));
    }

    #[test]
    fn try_with_stack_matrix_supports_zero_dimension() {
        let got = try_with_stack_matrix!(0usize, |m| -> Result<Option<f64>, LaError> {
            m.det_direct()
        });

        assert_eq!(got, Ok(Some(1.0)));
    }

    #[test]
    fn try_with_interval_matrix_supports_zero_dimension() {
        let got = try_with_interval_matrix!(0usize, |matrix| -> Result<
            IntervalDeterminantSign,
            LaError,
        > { matrix.det_sign() },);

        assert_eq!(got, Ok(IntervalDeterminantSign::Positive));
    }

    #[test]
    fn try_with_stack_matrix_evaluates_dimension_once() {
        let mut evaluations = 0;
        let got = try_with_stack_matrix!(
            {
                evaluations += 1;
                2usize
            },
            |matrix| -> Result<f64, LaError> { matrix.try_get(1, 1) },
        );

        assert_eq!(evaluations, 1);
        assert_eq!(got, Ok(0.0));
    }

    #[test]
    fn try_with_interval_matrix_evaluates_dimension_once() {
        let mut evaluations = 0;
        let got = try_with_interval_matrix!(
            {
                evaluations += 1;
                2usize
            },
            |matrix| -> Result<Interval, LaError> { matrix.try_get(1, 1) },
        );

        assert_eq!(evaluations, 1);
        assert_eq!(got, Ok(Interval::ZERO));
    }

    #[test]
    fn try_with_stack_matrix_reports_unsupported_dimension() {
        let got = try_with_stack_matrix!(8usize, |m| -> Result<f64, LaError> { m.det() });

        assert_eq!(
            got,
            Err(LaError::UnsupportedDimension {
                requested: 8,
                max: MAX_STACK_MATRIX_DISPATCH_DIM,
            })
        );
    }

    #[test]
    fn try_with_interval_matrix_reports_unsupported_dimension() {
        let got = try_with_interval_matrix!(8usize, |matrix| -> Result<
            IntervalDeterminantSign,
            LaError,
        > { matrix.det_sign() },);

        assert_eq!(
            got,
            Err(LaError::UnsupportedDimension {
                requested: 8,
                max: MAX_INTERVAL_MATRIX_DIM,
            })
        );
    }

    #[derive(Debug, PartialEq)]
    struct DownstreamError(LaError);

    impl From<LaError> for DownstreamError {
        fn from(err: LaError) -> Self {
            Self(err)
        }
    }

    #[test]
    fn try_with_stack_matrix_converts_unsupported_dimension_error() {
        let got = try_with_stack_matrix!(9usize, |m| -> Result<usize, DownstreamError> {
            assert_abs_diff_eq!(m.norm_inf()?, 0.0, epsilon = 0.0);
            Ok(0)
        });

        assert_eq!(
            got,
            Err(DownstreamError(LaError::UnsupportedDimension {
                requested: 9,
                max: MAX_STACK_MATRIX_DISPATCH_DIM,
            }))
        );
    }

    #[test]
    fn try_with_interval_matrix_converts_unsupported_dimension_error() {
        let got = try_with_interval_matrix!(8usize, |matrix| -> Result<
            IntervalDeterminantSign,
            DownstreamError,
        > { Ok(matrix.det_sign()?) },);

        assert_eq!(
            got,
            Err(DownstreamError(LaError::UnsupportedDimension {
                requested: 8,
                max: MAX_INTERVAL_MATRIX_DIM,
            }))
        );
    }

    #[cfg(feature = "exact")]
    #[test]
    fn try_with_rational_matrix_reports_unsupported_dimension() {
        let got = try_with_rational_matrix!(9usize, |matrix| -> Result<BigRational, LaError> {
            Ok(matrix.det())
        });

        assert_eq!(
            got,
            Err(LaError::UnsupportedDimension {
                requested: 9,
                max: MAX_RATIONAL_MATRIX_DISPATCH_DIM,
            })
        );
    }

    #[cfg(feature = "exact")]
    #[test]
    fn try_with_rational_matrix_converts_unsupported_dimension_error() {
        let got =
            try_with_rational_matrix!(9usize, |matrix| -> Result<BigRational, DownstreamError> {
                Ok(matrix.det())
            });

        assert_eq!(
            got,
            Err(DownstreamError(LaError::UnsupportedDimension {
                requested: 9,
                max: MAX_RATIONAL_MATRIX_DISPATCH_DIM,
            }))
        );
    }
}