The data cube itself is like a Fortran three-dimensional matrix.
Its location in the computer file system is denoted by
```in=PATHNAME`''
where
```in=`'' is the literal occurrance of those three letters
and
```PATHNAME`''
is a directory tree location like
``/sep/professor/pvi/data/western73.F''.
Like the Fortran cube, the cube can be real, complex,
double precision, or byte,
and these cases are distinguished by the element size in bytes.
Thus the history file contains one of
```esize=4`'',
```esize=8`'', or
```esize=1`''.
Embedded blanks around the ``='' are always forbidden.
The cube values are binary information;
they cannot be printed or edited
(without the intervention of something like a fortran ``format'').
To read and write cubes, see the manual pages for such routines
as `reed, sreed, rite, srite, snap`.

A cube has three axes.
The number of points on the 1-axis is `n1`.
A fortran declaration of a cube can be
`real mydata(n1,n2,n3)`.
For a plane, `n3=1`, and for a line, `n2=1`,
and many programs take ``1'' as the default for an undefined value of
`n2` or `n3`.
The physical location of the single data value
`mydata(1,1,1)`,
like a mathematical origin
(*o _{1}*,

Each axis has a label and naturally these labels are called
`label1`,
`label2`, and
`label3`.
Examples of labels are
`kilometers`,
`sec`,
`Hz`, and
`"offset, km"`.
Most often, `label1="time, sec"`.
Altogether that is parameters,
and there is an optional title parameter
that is interpreted by most of the plot programs.
An example is ``title="Yilmaz and Cumro Canada profile 25"`'.
We reserve the names `n4,o4,d4,label4`,
(a few programs support them already)
and please don't use `n5` etc
for anything but a 5-dimensional cubic lattice.

12/18/1997