Re-introduce knitro context closure and export solver quantities (#633)

* code: re-introduce knitro context closure and export solver quantities

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* code: place quantities calculation elsewhere

* code: place quantities calculation elsewhere

* code: add new quantities extracted from knitro context

* code: add int

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* code: add release notes

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Fabian Hofmann <fab.hof@gmx.de>

Author: 3 people

doc/release_notes.rst

@@ -25,6 +25,7 @@ Upcoming Version
 * Fix Xpress IIS label mapping for masked constraints and add a regression test for matching infeasible coordinates.
 * Enable quadratic problems with SCIP on windows.
 * Add ``fix()``, ``unfix()``, and ``fixed`` to ``Variable`` and ``Variables`` for fixing variables to values via equality constraints. Supports automatic rounding and optional integrality relaxation (``relax=True``) for MILP dual extraction.
+* Free the knitro context and compute necessary quantities within linopy. Knitro context is not exposed anymore.
 
 
 Version 0.6.5

linopy/solvers.py

@@ -1747,7 +1747,10 @@ def get_solver_solution() -> Solution:
         return Result(status, solution, m)
 
 
-KnitroResult = namedtuple("KnitroResult", "knitro_context reported_runtime")
+KnitroResult = namedtuple(
+    "KnitroResult",
+    "reported_runtime mip_relaxation_bnd mip_number_nodes mip_number_solves mip_rel_gap mip_abs_gap abs_feas_error rel_feas_error abs_opt_error rel_opt_error n_vars n_cons n_integer_vars n_continuous_vars",
+)
 
 
 class Knitro(Solver[None]):
@@ -1895,8 +1898,38 @@ def solve_problem_from_file(
             ret = int(knitro.KN_solve(kc))
 
             reported_runtime: float | None = None
+            mip_relaxation_bnd: float | None = None
+            mip_number_nodes: int | None = None
+            mip_number_solves: int | None = None
+            mip_rel_gap: float | None = None
+            mip_abs_gap: float | None = None
+            abs_feas_error: float | None = None
+            rel_feas_error: float | None = None
+            abs_opt_error: float | None = None
+            rel_opt_error: float | None = None
+            n_vars: int | None = None
+            n_cons: int | None = None
+            n_integer_vars: int | None = None
+            n_continuous_vars: int | None = None
             with contextlib.suppress(Exception):
                 reported_runtime = float(knitro.KN_get_solve_time_real(kc))
+                mip_relaxation_bnd = float(knitro.KN_get_mip_relaxation_bnd(kc))
+                mip_number_nodes = int(knitro.KN_get_mip_number_nodes(kc))
+                mip_number_solves = int(knitro.KN_get_mip_number_solves(kc))
+                mip_rel_gap = float(knitro.KN_get_mip_rel_gap(kc))
+                mip_abs_gap = float(knitro.KN_get_mip_abs_gap(kc))
+                abs_feas_error = float(knitro.KN_get_abs_feas_error(kc))
+                rel_feas_error = float(knitro.KN_get_rel_feas_error(kc))
+                abs_opt_error = float(knitro.KN_get_abs_opt_error(kc))
+                rel_opt_error = float(knitro.KN_get_rel_opt_error(kc))
+                n_vars = int(knitro.KN_get_number_vars(kc))
+                n_cons = int(knitro.KN_get_number_cons(kc))
+                var_types = list(knitro.KN_get_var_types(kc))
+                n_integer_vars = int(
+                    var_types.count(knitro.KN_VARTYPE_INTEGER)
+                    + var_types.count(knitro.KN_VARTYPE_BINARY)
+                )
+                n_continuous_vars = int(var_types.count(knitro.KN_VARTYPE_CONTINUOUS))
 
             if ret in CONDITION_MAP:
                 termination_condition = CONDITION_MAP[ret]
@@ -1941,12 +1974,26 @@ def get_solver_solution() -> Solution:
             return Result(
                 status,
                 solution,
-                KnitroResult(knitro_context=kc, reported_runtime=reported_runtime),
+                KnitroResult(
+                    reported_runtime=reported_runtime,
+                    mip_relaxation_bnd=mip_relaxation_bnd,
+                    mip_number_nodes=mip_number_nodes,
+                    mip_number_solves=mip_number_solves,
+                    mip_rel_gap=mip_rel_gap,
+                    mip_abs_gap=mip_abs_gap,
+                    abs_feas_error=abs_feas_error,
+                    rel_feas_error=rel_feas_error,
+                    abs_opt_error=abs_opt_error,
+                    rel_opt_error=rel_opt_error,
+                    n_vars=n_vars,
+                    n_cons=n_cons,
+                    n_integer_vars=n_integer_vars,
+                    n_continuous_vars=n_continuous_vars,
+                ),
             )
-
         finally:
-            # Intentionally keep the Knitro context alive; do not free `kc` here.
-            pass
+            with contextlib.suppress(Exception):
+                knitro.KN_free(kc)
 
 
 mosek_bas_re = re.compile(r" (XL|XU)\s+([^ \t]+)\s+([^ \t]+)| (LL|UL|BS)\s+([^ \t]+)")