A simple signum function


The other day I needed to compute the signum function for each element of a matrix. If x is a real number, then the sgn(x) is -1 when x<0, 1 when x>0, and 0 when x=0.

I wrote a SAS/IML module that contains a compact little expression:

proc iml;
start sgn(x);
   return( (x>=0) - (x<=0) );

However, even before I tested the function, I heard a little voice inside my head calling "I'll bet SAS already has this function...." A short search later, and I had discovered the built-in SIGN function:

x = {-3 2  0,
      5 0  7,
     -2 1 -5 };
s = sign(x);
print s;

Lessons learned:


About Author

Rick Wicklin

Distinguished Researcher in Computational Statistics

Rick Wicklin, PhD, is a distinguished researcher in computational statistics at SAS and is a principal developer of SAS/IML software. His areas of expertise include computational statistics, simulation, statistical graphics, and modern methods in statistical data analysis. Rick is author of the books Statistical Programming with SAS/IML Software and Simulating Data with SAS.

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