Enum DeclaredHessianForm 

pub enum DeclaredHessianForm {
    Dense,
    Operator {
        materialization: OuterHessianMaterialization,
        estimated_materialization_cost: Option<f64>,
    },
    Either,
    Unavailable,
}

Capability-time declaration of what shape the outer Hessian takes. Replaces the binary Derivative for the Hessian field on OuterCapability: callers that know the shape upfront declare it here, and the planner routes between dense ARC and matrix-free trust-region before seed evaluation rather than dynamically branching on seed_eval.hessian at runtime.

Variants:

• Dense: the family always returns HessianResult::Analytic(_). The planner picks dense ARC; matrix-free TR is never engaged.
• Operator { materialization, estimated_materialization_cost }: the family always returns HessianResult::Operator(_). The planner picks matrix-free TR unless materialization advertises Explicit/BatchedHvp cheaply enough that materializing once per outer iter (opt 0.4.2 with_materialize_when_cheap) wins. estimated_materialization_cost is reserved for a future cost model; today it is purely informational.
• Either: the family may return either shape; the runner inspects the seed eval and locks the route then. This is the historical default for code paths where Derivative::Analytic made the declaration and the seed loop branched on seed_eval.hessian.
• Unavailable: no analytic Hessian. The planner picks BFGS / EFS per the gradient declaration and the rest of the capability.

Variants

Dense

Operator

Fields

materialization: OuterHessianMaterialization

estimated_materialization_cost: Option<f64>

Either

Unavailable

Implementations

impl DeclaredHessianForm

pub const fn is_analytic(self) -> bool

Coarse “is an analytic Hessian declared?” projection. true for Dense / Operator / Either; false for Unavailable. Used by plan to keep the existing Derivative-based match arms while richer routing decisions consult the form directly.

pub const fn is_operator_only(self) -> bool

True when the declaration commits to a matrix-free path.

pub const fn is_dense_only(self) -> bool

True when the declaration commits to a dense path.

Trait Implementations

impl Clone for DeclaredHessianForm

fn clone(&self) -> DeclaredHessianForm

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for DeclaredHessianForm

impl Debug for DeclaredHessianForm

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

Formats the value using the given formatter.

impl PartialEq for DeclaredHessianForm

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for DeclaredHessianForm