Fix Poisson solver: LinearProblem compatibility for different dolfinx versions

backend/poisson/solver.py

@@ -103,15 +103,21 @@ def solve_poisson(params: Dict[str, Any]) -> Dict[str, Any]:
         L = L + ufl.inner(g, v) * ds
     
     # 5. Résolution
-    problem = LinearProblem(
-        a, L,
-        bcs=bcs,
-        petsc_options_prefix="poisson",
-        petsc_options={
-            "ksp_type": "preonly",
-            "pc_type": "lu",
-        },
-    )
+    # Essayer avec petsc_options_prefix (versions récentes de dolfinx)
+    # sinon sans (versions plus anciennes)
+    try:
+        problem = LinearProblem(
+            a, L,
+            bcs=bcs,
+            petsc_options_prefix="poisson",
+            petsc_options={
+                "ksp_type": "preonly",
+                "pc_type": "lu",
+            },
+        )
+    except TypeError:
+        # Version ancienne de dolfinx sans petsc_options_prefix
+        problem = LinearProblem(a, L, bcs=bcs)
     uh = problem.solve()
     
     computation_time = time.time() - start_time