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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 simulate(self, n):
 """ Evolve multiple sites during one tree traversal """

        self.tree._tree.seed_node.states = self.ancestral_states(n)
        categories = np.random.randint(self.ncat, size=n).astype(np.intc)

        for node in self.tree.preorder(skip_seed=True):
            node.states = self.evolve_states(node.parent_node.states, categories, node.pmats)
            if node.is_leaf():
                self.sequences[node.taxon.label] = node.states
        return self.sequences_to_string()