请问一下这个排列组合函数，是怎么得到的？里面每个函数的意义是什么？
=IF(ROW()-ROW($D$2)+1>COUNTA($A$2:$A$5)*COUNTA($B$2:$B$4),"",INDEX($A$2:$A$5,INT((ROW()-ROW($D$2))/COUNTA($B$2:$B$4)+1))&"-"&INDEX($B$2:$B$4,MOD(ROW()-ROW($D$2),COUNTA($B$2:$B$4))+1))
=IF(ROW()-ROW($D$2)+1>COUNTA($A$2:$A$5)*COUNTA($B$2:$B$4),"",INDEX($A$2:$A$5,INT((ROW()-ROW($D$2))/COUNTA($B$2:$B$4)+1))&"-"&INDEX($B$2:$B$4,MOD(ROW()-ROW($D$2),COUNTA($B$2:$B$4))+1))