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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def subgraph(self, vertices):
 r"""Create a subgraph from a list of vertices. Parameters vertices : list Vertices to keep. Either a list of indices or an indicator function. Returns ------- subgraph : :class:`Graph` Subgraph. Examples -------- array([[0., 0., 3.], [0., 0., 4.], [3., 4., 0.]]) """

        adjacency = self.W[vertices, :][:, vertices]
        try:
            coords = self.coords[vertices]
        except AttributeError:
            coords = None
        graph = Graph(adjacency, self.lap_type, coords, self.plotting)
        for name, signal in self.signals.items():
            graph.set_signal(signal[vertices], name)
        return graph