<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def evals(self):
 """ The eigenvalues of the parameter space. This is a Dictionary of numpy.array Each entry in the dictionary corresponds to the different frequency ranges described in vary_fmax. If vary_fmax = False, the only entry will be f_upper, this corresponds to integrals in [f_low,f_upper). This entry is always present. Each other entry will use floats as keys to the dictionary. These floats give the upper frequency cutoff when it is varying. Each numpy.array contains the eigenvalues which, with the eigenvectors in evecs, are needed to rotate the coordinate system to one in which the metric is the identity matrix. """

        if self._evals is None:
            errMsg = "The metric eigenvalues have not been set in the "
            errMsg += "metricParameters instance."
            raise ValueError(errMsg)
        return self._evals