pounce-sens-core

The engine-agnostic core of POUNCE's sensitivity layer: the SensBacksolver contract and everything that can be built on it without knowing which solver produced the KKT system.

What is here

Everything in this crate is written against one trait — SensBacksolver, whose entire required surface is dim() and solve(rhs, lhs). Any engine that can back-solve against its converged factor gets the rest for free:

module	what it provides
`backsolver`	the `SensBacksolver` contract, `BoundRow`, and the synthetic `DenseLuBacksolver` that validates the math without an IPM
`boundcheck`	fix-relax refinement, path following through active-set breakpoints, the directional derivative at a kink
`sens_app`	the sIPOPT `SensApplication` driver, reduced-Hessian entry point, option registration
`p_calculator`, `schur_data`, `schur_driver`, `step_calc`, `reduced_hessian`	the `P = K⁻¹A` / Schur-complement stack

Two consumers exist in tree. pounce-sensitivity implements the trait over the NLP filter-IPM's KKT factor; pounce-convex implements it over the convex active-set KKT. Neither depends on the other, and this crate depends on neither — only on pounce-common and pounce-linalg.

What is deliberately not here

Two parts of the NLP arm's sensitivity layer are genuinely engine-coupled and stay in pounce-sensitivity, so the boundary is a decision rather than an oversight:

The corrector. Its entry points take the concrete PdSensBacksolver and reach for activity_handles(), offsets_public(), block_dims(), pack_natural() and corrector_sigma() — none on the trait, several meaningful only for the filter-IPM's eight-block compound iterate.
Activity classification's plumbing. It reads the filter-IPM's own iterate (z_l, z_u, v_l, v_u) out of an IpoptData handle. Its pure decision rule is portable; the plumbing around it is not.

Generalizing either means abstracting IpoptData / CalculatedQuantities access behind another trait — a larger project than this crate.

Algorithmic reference

Pirnay, H., López-Negrete, R., and Biegler, L.T. (2012). Optimal sensitivity based on IPOPT. Mathematical Programming Computation, 4(4), 307–331. DOI: 10.1007/s12532-012-0043-2.

Upstream source

The port follows the upstream sIPOPT contrib at ref/Ipopt/contrib/sIPOPT/src/ in this repo (EPL-2.0, © Hans Pirnay 2009–2011 per the headers). The files mapped here moved out of pounce-sensitivity when this crate was split off; the mapping is unchanged:

pounce-sens-core	upstream
`src/schur_data.rs` — `SchurData` trait	`SensSchurData.hpp` (lines 17–177)
`src/schur_data.rs` — `IndexSchurData`	`SensIndexSchurData.{hpp,cpp}`
`src/p_calculator.rs` — `PCalculator` trait	`SensPCalculator.hpp` (lines 17–133)
`src/backsolver.rs` — `SensBacksolver` trait	`SensBacksolver.hpp`

Every public item in this crate documents the upstream symbol it mirrors, with line numbers when they're stable.

License