Struct MinSettings 

pub struct MinSettings {
    pub x_tol_abs: f64,
    pub x_tol_rel: f64,
    pub max_iterations: u32,
}

Convergence tolerance on the bracket width, and the iteration cap.

A lane is converged when the bracket has shrunk to x_tol_abs + x_tol_rel * |x_mid|, where x_mid is the current bracket midpoint. There is no function-value tolerance — see the module-level “Convergence is on the BRACKET, never on the value” section for why one would be actively misleading here.

Fields and valid ranges

• x_tol_abs — absolute abscissa tolerance, in the abscissa’s own units. Must be >= 0. Guards the case x* ≈ 0, where a purely relative tolerance can never be met.
• x_tol_rel — relative abscissa tolerance, dimensionless, >= 0. Values below SQRT_EPSILON are honoured but buy no accuracy on a smooth objective; they only cost iterations.
• max_iterations — hard cap. On reaching it a lane reports MinStatus::MaxIterations and its current bracket midpoint, which MinSolution::extremum still refuses to hand out. Must be >= 1.

A negative tolerance is not rejected; it simply can never be met, and the lane will report MinStatus::MaxIterations. That is a truthful outcome rather than a silent success.

Defaults, and why they differ from crate::math::parallel::RootSettings

x_tol_abs = 1e-12, x_tol_rel = SQRT_EPSILON = 1.4901161193847656e-8, max_iterations = 200.

The relative tolerance is ~10 000x looser than the root finder’s 1e-12, and that is not a lowered standard — it is the accuracy a derivative-free minimiser can actually deliver on a smooth objective (module docs, “Achievable accuracy”). Defaulting to a far tighter tolerance would spend about 30 extra iterations per lane narrowing a bracket whose midpoint does not improve — measured 2026-08-13: 40-47 iterations at these defaults against 77 at x_tol_abs = 1e-15, x_tol_rel = 0 on the same 64-lane batch, for a worst abscissa error that stays at 1.05e-8 either way.

The iteration cap is 200 rather than 100 because golden section contracts by a fixed factor of GOLDEN_RATIO per iteration — it has no superlinear phase to bail it out. Reaching a relative 1.5e-8 from a bracket 1e14 times wider than the answer costs ln(1e-14)/ln(0.618) ≈ 67 iterations; 200 leaves room for a caller that tightens the tolerance well past the useful floor.

Example

use outram_foam_basic_lib::math::minimise::{MinSettings, SQRT_EPSILON};

// Struct-update syntax keeps the defaults you did not mean to change.
let s = MinSettings {
    max_iterations: 500,
    ..MinSettings::default()
};
assert_eq!(s.x_tol_rel, SQRT_EPSILON);
assert_eq!(s.max_iterations, 500);

// The steam-tables choked-flow caller's rule -- a 1 Pa bracket -- expressed
// as an absolute tolerance with the relative part switched off.
let one_pascal = MinSettings { x_tol_abs: 1.0, x_tol_rel: 0.0, max_iterations: 100 };
assert_eq!(one_pascal.bracket_tolerance(5.0e6), 1.0);

Fields

x_tol_abs: f64

Absolute bracket-width tolerance, in the abscissa’s units. >= 0.

x_tol_rel: f64

Relative bracket-width tolerance, dimensionless. >= 0.

max_iterations: u32

Maximum iterations per lane before reporting MinStatus::MaxIterations. >= 1.

Implementations

impl MinSettings

pub fn bracket_tolerance(&self, x: f64) -> f64

The bracket-width tolerance at abscissa x: x_tol_abs + x_tol_rel * |x|.

Arguments

• x — the abscissa at which to evaluate the tolerance, in the abscissa’s units. The kernel passes the current bracket midpoint.

Returns

A width in the abscissa’s units.

Trait Implementations

impl Clone for MinSettings

fn clone(&self) -> MinSettings

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for MinSettings

impl Debug for MinSettings

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for MinSettings

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq for MinSettings

fn eq(&self, other: &MinSettings) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for MinSettings