An orthogonal array OA
is a 
array with entries taken from an 
-set 
having the property that in any two rows, each ordered pair
of symbols from 
occurs exactly once.
Orthogonal Array
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References
Colbourn, C. J. and Dinitz, J. H. (Eds.). CRC Handbook of Combinatorial Designs. Boca Raton, FL: CRC Press, p. 111, 1996.Hedayat, A. S.; Sloane, N. J. A.; and Stufken, J. Orthogonal Arrays: Theory and Applications. New York: Springer-Verlag, 1999.Referenced on Wolfram|Alpha
Orthogonal ArrayCite this as:
Weisstein, Eric W. "Orthogonal Array." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/OrthogonalArray.html