A dyadic, also known as a vector direct product , is a linear polynomial of dyads consisting of nine components
which transform as

Dyadics are often represented by Gothic capital letters. The use of dyadics is nearly archaic since tensors perform the same function but are
notationally simpler.

A unit dyadic is also called the idemfactor and is defined such that

(4)

In Cartesian coordinates ,

(5)

and in spherical coordinates

(6)

See also Dyad ,

Tensor ,

Tetradic ,

Vector
Direct Product
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References Arfken, G. "Dyadics." §3.5 in Mathematical Methods for Physicists, 3rd ed. Orlando, FL: Academic Press, pp. 137-140,
1985. Jeffreys, H. and Jeffreys, B. S. "Dyadic Notation."
§3.04 in Methods
of Mathematical Physics, 3rd ed. Cambridge, England: Cambridge University
Press, p. 89, 1988. 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. Referenced
on Wolfram|Alpha Dyadic
Cite this as:
Weisstein, Eric W. "Dyadic." From MathWorld --A
Wolfram Web Resource. https://mathworld.wolfram.com/Dyadic.html

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