11 elements in DESCA, DESCB and DESCC?

[lanczos]

I notice that in PDGEMM the descriptor arrays DESC have been changed to contain 11 elements. The two new elements are IMB_A and INB_A. I do not quite undertand what they exactly mean. Could someone explain or show me a pictorial illustration? I searched the web but did not see any discussions. On the other hand, the tool DESCINIT is not updated with the two new elements. I am confused.