[…] Suppose you have a set of 2-D points. How can you identify the quadrant for each point? One way is to use the SIGN function in SAS, which returns the value -1 if a value is negative, +1 if the value is positive, and 0 if the value is 0. The SIGN function in the DATA step takes a scalar argument, but recall that you can call Base SAS functions from PROC IML and pass in vectors or matrices. …