Hi Ric,

Very useful article - thanks.

I think I found two minor errors. In the true matrix multiplication paragraph you wrote "...where the number of rows of u matches the number of columns of v,...". I think rows and columns should be the other way round if you multiply u*v.

Second, the HDIR function didn’t like the transposed first vector when I tried your example. hdir(u, v) worked for me (SAS 9.3).