Fix SupervisedSolver GPU bug and implement GraphSolver (#346)

* Fix some bugs
* Solve bug with GPU and model_summary parameters in SupervisedSolver class
* Implement GraphSolver class
* Fix Tutorial 5

pina/solvers/graph.py

@@ -0,0 +1,34 @@
+from .supervised import SupervisedSolver
+from ..graph import Graph
+
+
+class GraphSupervisedSolver(SupervisedSolver):
+
+    def __init__(
+        self,
+        problem,
+        model,
+        nodes_coordinates,
+        nodes_data,
+        loss=None,
+        optimizer=None,
+        scheduler=None):
+        super().__init__(problem, model, loss, optimizer, scheduler)
+        if isinstance(nodes_coordinates, str):
+            self._nodes_coordinates = [nodes_coordinates]
+        else:
+            self._nodes_coordinates = nodes_coordinates
+        if isinstance(nodes_data, str):
+            self._nodes_data = nodes_data
+        else:
+            self._nodes_data = nodes_data
+
+    def forward(self, input):
+        input_coords = input.extract(self._nodes_coordinates)
+        input_data = input.extract(self._nodes_data)
+
+        if not isinstance(input, Graph):
+            input = Graph.build('radius', nodes_coordinates=input_coords, nodes_data=input_data, radius=0.2)
+        g = self.model(input.data, edge_index=input.data.edge_index)
+        g.labels = {1: {'name': 'output', 'dof': ['u']}}
+        return g