def METHOD_NAME(self, scales):
    """
    Set the scale of the mulipliers for the two proposal kernel
    covariance matrices. Must be of the form ``[scale_1, scale_2]``.
    """
    if len(scales) != 2:
        raise ValueError('Scales must be of length 2.')
    for scale in scales:
        if scale <= 0:
            raise ValueError('Scales must be positive.')
    self._sigma_scale = [scales[0], scales[1]]
    self._sigma = [self._sigma_scale[i] * self._sigma_base
                   for i in range(self._n_kernels)]