THE DATA CUBE

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 occurrence of those three characters, and PATHNAME is a directory tree location like /sep/professor/pvi/data/western73.F. Like the Fortran cube, the data 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, respectively. 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 could be real mydata(n1,n2,n3). For a plane, n3=1, and for a line, n2=1. In addition, 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 (o₁,o₂,o₃), is denoted by the three real variables o1, o2, and o3. The data-cube values are presumed to be uniformly spaced along these axes like the mathematical increments $(\Delta_1,\Delta_2,\Delta_3)$,which may be negative and are denoted by the three real variables d1, d2, and d3.

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 $2+3\times 4$ 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, and label4 (a few programs support them already), and please do not use n5 etc. for anything but a five-dimensional cubic lattice.