The class of second order tensors (aka tensors). Given an orthornormal basis a dyad can be decomposed into scalar components. These components can be represented as a square matrix. The matrix is not unique but it a 'view' of the tensor for a particular basis.
(<=> (Dyad ?D)
(And (Constant-Quantity ?D)
(Tensor-Quantity ?D)
(= (Tensor-Order ?D) 2)
(Forall (?B ?I ?J)
(=> (And (Orthonormal-Basis ?B)
(= (Basis.Dimension ?B)
(Spatial.Dimension ?D))
(Positive-Integer ?I)
(=< ?I (Spatial.Dimension ?D))
(Positive-Integer ?J)
(=< ?J (Spatial.Dimension ?D)))
(And (Defined (Dyad-Component ?D ?I ?J ?B))
(= (Quantity.Dimension (Dyad-Component ?D
?I
?J
?B))
(Quantity.Dimension ?D)))))
(Forall (?U)
(=> (And (Unit-Of-Measure ?U)
(= (Quantity.Dimension ?U)
(Quantity.Dimension ?D)))
(Numeric-Tensor (Magnitude ?D ?U))))))