def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def update_cost_model(self, x, cost_x):
        """
        Updates the GP used to handle the cost.

        param x: input of the GP for the cost model.
        param x_cost: values of the time cost at the input locations.
        """

        if self.cost_type == 'evaluation_time':
            cost_evals = np.log(np.atleast_2d(np.asarray(cost_x)).T)

            if self.num_updates == 0:
                X_all = x
                costs_all = cost_evals
            else:
                X_all = np.vstack((self.cost_model.model.X,x))
                costs_all = np.vstack((self.cost_model.model.Y,cost_evals))

            self.num_updates += 1
            self.cost_model.updateModel(X_all, costs_all, None, None)