05-06-2014 09:57 AM
What have you tried? To get started, read about subscripts in the doc: SAS/IML(R) 13.1 User's Guide .
In particular, study the example that uses the colon operator ( to form indices and to extract a subset of a matrix or vector: After you understand the example, use the fact that you can create an vector in reverse order like this: 3:1. Investigate what happens if you use 3:1 as an index into your vector.