add gurobipy direct implementation

Author: coroa

linopy/io.py

@@ -751,6 +751,23 @@ def to_gurobipy(
         c = model.addMConstr(M.A, x, M.sense, M.b)  # type: ignore
         c.setAttr("ConstrName", list(names))  # type: ignore
 
+    if m.variables.sos:
+        for var_name in m.variables.sos:
+            var = m.variables.sos[var_name]
+            sos_type = var.attrs["sos_type"]
+            sos_dim = var.attrs["sos_dim"]
+
+            def add_sos(s):
+                s = s.squeeze()
+                model.addSOS(sos_type, x[s].tolist(), s.coords[sos_dim].values)
+
+            others = tuple(dim for dim in var.labels.dims if dim != sos_dim)
+            if not others:
+                add_sos(var.labels)
+            else:
+                for _, s in var.labels.groupby(*others):
+                    add_sos(s)
+
     model.update()
     return model
 

linopy/model.py

@@ -576,10 +576,17 @@ def add_sos_constraints(
             raise ValueError(f"sos_dim must name a variable dimension, got {sos_dim}")
 
         if "sos_type" in variable.attrs or "sos_dim" in variable.attrs:
-            sos_type = variable.attrs.get("sos_type")
-            sos_dim = variable.attrs.get("sos_dim")
+            existing_sos_type = variable.attrs.get("sos_type")
+            existing_sos_dim = variable.attrs.get("sos_dim")
             raise ValueError(
-                "variable already has an sos{sos_type} constraint on {sos_dim}"
+                f"variable already has an sos{existing_sos_type} constraint on {existing_sos_dim}"
+            )
+
+        # Validate that sos_dim coordinates are numeric (needed for weights)
+        if not pd.api.types.is_numeric_dtype(variable.coords[sos_dim]):
+            raise ValueError(
+                f"SOS constraint requires numeric coordinates for dimension '{sos_dim}', "
+                f"but got {variable.coords[sos_dim].dtype}"
             )
 
         variable.attrs.update(sos_type=sos_type, sos_dim=sos_dim)