Dyads extend Vectors to provide an alternative description to second Rank
Tensors. A dyad
of a pair of Vectors and is
. The Dot Product is defined by
Morse, P. M. and Feshbach, H. ``Dyadics and Other Vector Operators.'' §1.6 in
Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 54-92, 1953.