Function IpoptSolverReducedHessian 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn IpoptSolverReducedHessian(
    solver: IpoptSolver,
    n_pins: Index,
    pin_indices: *const Index,
    obj_scal: Number,
    hr_out: *mut Number,
) -> Bool

Reduced Hessian H_R = obj_scal · B K⁻¹ Bᵀ over the pinned rows. hr_out receives an n_pins²-long column-major dense matrix.

Returns TRUE on success, FALSE otherwise.

Safety

pin_indices must point to n_pins valid elements; hr_out must point to at least n_pins² Number slots.