Two-point tensor
Two-point tensors are tensor-like quantities which transform as vectors with respect to each of their indices and are used in continuum mechanics to transform between reference ("material") and present ("configuration") coordinates.
As with many applications of tensors, Einstein summation notation is frequently used. To clarify this notation, capital indicies are often used to indicate reference coordinates and lowercase for present coordinates. Thus, a two-point tensor will have one capital and one lower-case index; for example, AjM.