Find all the segments in the triangulation and return an
        array of vertices (n1,n2) where n1 < n2

def identify_segments(self):
        """
        Find all the segments in the triangulation and return an
        array of vertices (n1,n2) where n1 < n2
        """

        lst  = self.lst
        lend = self.lend
        lptr = self.lptr

        segments_array = np.empty((len(lptr),2),dtype=np.int)
        segments_array[:,0] = lst[:] - 1
        segments_array[:,1] = lst[lptr[:]-1] - 1

        valid = np.where(segments_array[:,0] < segments_array[:,1])[0]
        segments = segments_array[valid,:]

        return self._deshuffle_simplices(segments)