For a primal-infeasible LP, returns the dual unbounded ray: a Farkas certificate of primal infeasibility, with one entry per constraint (row).
hi_solver_get_dual_ray(solver)A list with `status` (integer, 0 = OK), `has_dual_ray` (logical), and `dual_ray` (numeric vector of length `n_row`, or `NULL` when no ray exists).
An object of class "highs_solver".
A dual ray is available only after an LP detected to be **infeasible** and solved by the **simplex** method (the interior-point solver does not produce a ray). Disable presolve, or rely on HiGHS's postsolve, to recover the ray on the original model. Requesting the ray may solve an auxiliary LP.