Calculate Mipgap in the meta results

AUTHORS.rst

@@ -28,6 +28,7 @@ Authors
 * Jonathan Amme
 * Julian Endres
 * Lluis Millet
+* Lena Rosin
 * Lennart Schürmann
 * Martin Soethe
 * Marie-Claire Gering

CITATION.cff

@@ -170,4 +170,8 @@ authors:
     family-names: Gering
     given-names: Marie-Claire
     alias: "@MaGering"
+  -
+    family-names: Rosin
+    given-names: Lena
+    alias: "@leroum"
 ...

docs/whatsnew/v0-5-6.rst

@@ -5,6 +5,7 @@ Bug fixes
 #########
 
 * Update required Pyomo version to allow working with numpy >= 2.0.0.
+* Mipgap is calculated in the meta results
 
 Known issues
 ############
@@ -15,3 +16,4 @@ Contributors
 ############
 
 * Patrik Schönfeldt
+* Lena Rosin

src/oemof/solph/processing.py

@@ -481,6 +481,13 @@
                     meta_res[k1][k2] = msg.format(
                         type(om.es.results[k1][0][k2])
                     )
+    try:
+        meta_res["problem"]["MIPGap"] = (
+            meta_res["problem"]["Upper bound"]
+            - meta_res["problem"]["Lower bound"]
+        ) / meta_res["problem"]["Lower bound"]
+    except KeyError:
+        pass
 
     return meta_res
 

tests/test_processing.py

@@ -87,6 +87,19 @@ def setup_class(cls):
         cls.mod = Model(cls.es)
         cls.mod.solve()
 
+    def test_mipgap(self):
+        """Test that one can access the MIPGap."""
+        meta = processing.meta_results(self.om)
+        assert "MIPGap" in meta["problem"], (
+            'No "MIPGap" in `meta_results`.'
+            " Maybe you're using solver other than cbc or gurobi?"
+        )
+        assert meta["problem"]["MIPGap"] == 0, (
+            "Incorrect MIPGap value."
+            "\nExpected: `0`"
+            f"\nGot: `{meta['problem']['MIPGap']}`"
+        )
+
     def test_flows_with_none_exclusion(self):
         b_el2 = self.es.groups["b_el2"]
         demand = self.es.groups["demand_el"]