Vectors posses a dimensionality. A scalar is a vector of the lowest
dimensionality. Most vectors are one-dimensional lists of numbers.
Certain types of analysis produce multidimensional vectors, which are
analogous to arrays. This dimensionality is indicated when the
vectors are listed with the **display** command or the **let**
command without arguments. Plotting a multidimensional vector will
produce a family of traces. Elements and sub-dimensional vectors are
specified with multiple square brackets, with the bracket on the right
having the lowest dimensionality.

For example, one might issue the following command:

which will perform an ac analysis with the dc sources.ac dec 10 1Hz 1Mhz dc v1 0 2 .1 v2 4.5 5.5 .25

Vectors have an indexing that begins with 0, and an index, or range of
indices, can be specified in square brackets following the vector
name, for each dimension. The notation `[ lower,upper]`, where

Vectors typically have defined units. The units are carried through a
computation, and simplified when the result is generated. Presently,
the system can not handle fractional powers. The units of a vector
can be set with the **settype** command.