Vector quantities are written in bold typeface, e.g. 
, and
tensors are written in a bold sans serif typeface, e.g. x
. Unit
vectors are indicated by a caret placed over the symbol, e.g. 
is the unit vector parallel to 
. This convention is extended
in the usual fashion so that 
is the unit vector in the
direction of the coordinate x. When two vectors or tensors are written
sequentially, as in 
, it is implied that the tensor or
outer product is to be taken. This convention is extended so that 
means that 
is to be raised to the kth power with respect
to the tensor product. To indicate the square of the length of a vector,
the symbol is written in a plain type style, i.e. 
is a rank
two tensor (or dyad), whereas 
is the square of the length of 
. Moments of functions are are written with a superscript in
parentheses, e.g. 
.
These are lth rank tensor quantities that may also be considered as the
Taylor coefficients of the Fourier transform, 
.