I am reading a paper https://arxiv.org/abs/1910.07143 I am unable to understand the construction of table III, for the section Orthogonality and completeness of matrix elements in group space.
The theory behind it is given as
They have constructed 24x24 table stating the orthongonality and completeness of irr. reps matrix elements as the vector in group space. Please help me understand this. I am unable to determine what $U_{iuv}$ is...
I am also searching for the basic theory behind it. How does the group space looks like, where these matrices are the vectors. Is it the transformation matrix or the matrix for irreducible represenatations?
Any help would be great. Thanks in advance.