<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _maximize(self):
 """ Find argmax of the acquisition function."""

        if not self.space.is_observations_valid():
            return None
        y_max = self.space.y.max()
        self.utility_function.gaussian_process.fit(self.space.x, self.space.y)
        return self.utility_function.max_compute(y_max=y_max,
                                                 bounds=self.space.bounds,
                                                 n_warmup=self.n_warmup,
                                                 n_iter=self.n_iter)