  We study the relation between wavefunction (de)localization and the avoided
crossing in a quadrupole billiard. We employ the inverse participation ratio,
the Renyi entropy and the root-mean-square (rms) image contrast as the three
types of measures for wavefunction (de)localization. It is found that all these
measures behave similarly, exhibiting a minimum at the center of avoided
crossing, where wavefunction is maximally delocalized. Our results show that
these quantities can be good indicators for wavefunction (de)localization
although the rms contrast yields the most sensitive measure among them.
