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Triple Dot Product


The term triple dot product has distinct meanings in vector and tensor notation. An ordinary dot product is a binary operation that maps two vectors to a scalar, so a dot product of three vectors is not defined by associating the symbols as (a·b)·c: this would attempt to take the dot product of a scalar and a vector.

In vector algebra, "triple dot product" is sometimes used informally for the scalar triple product

 a·[b×c],

which uses one cross product and one dot product, not three dot products.

In tensor analysis, a triple dot denotes contraction over three pairs of indices. For third-rank tensors A and B with components A_(ijk) and B_(ijk), one convention gives the scalar

 A|B=sum_(i,j,k)A_(ijk)B_(kji).

(Verscharen et al. 2019). This is a tensor contraction of two tensors, not a product of three vectors.


See also

Cross Product, Dot Product, Scalar Triple Product, Tensor Contraction, Triple Product

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References

Gibbs, J. W. Vector Analysis. New York: Dover, 1960.Pride, S. R. "An Introduction to Tensor Calculus." Ch. 1 in An Introduction to Continuum Physics. Cambridge, England: Cambridge University Press, 2025.Verscharen, D.; Klein, K. G.; and Maruca, B. A. "The Multi-Scale Nature of the Solar Wind." Living Rev. Solar Phys. 16, Article 5, 2019. https://doi.org/10.1007/s41116-019-0021-0.

Cite this as:

Weisstein, Eric W. "Triple Dot Product." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/TripleDotProduct.html

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