A '''tensor''' in mathematics is a generalisation of vectors and matrices, where the number of indices can be any natural number (as opposed to 1 for vectors and 2 for matrices). The name comes from ''tension'', since the need for these first arose in the study of complex tensions, but they are probably most prominently seen in differential geometry.

[AM] (22 october) From my student days I remember a lecture on the transformation of the anisotropic properties of certain solids due to 
elastic forces that required the use of a fourth-order tensor, as the properties themselves were a matrix in three dimensions. That sort
of things involve 81 coefficients (3**4) but luckily there are all manner of requirements with respect to one another, so that the number of 
independent coefficients is much smaller.

Tensors also seem to figure prominently in general relativity theory (yes, differential geometry), but fortunately I have never been 
involved in that.

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'''Tensor''' is also the name of a package by Neil McKay.
[[Please provide links to code and documentation, fill in details, etc.]]

See also:
   * [PDEs and the Tensor package]

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