@Section
   @Title { Introduction }
   @Tag { grintro }
@Begin
@PP
The Lout definitions for graph formatting are kept in a file called
{@Code "graph"}, which you must include at the start of your document if
graph.file @Index { @Code "graph" file }
you want graphs, like this:
@ID @OneRow @Code {
"@SysInclude { graph }"
"@SysInclude { doc }"
"@Doc @Text @Begin"
"..."
"@End @Text"
}
Files of definitions, like {@Code "graph"}, must be included before the
setup file.  Alternatively, if you are using your own setup file, you may
place the include commands within it; the place to put them is clearly
marked in all the standard setup files.  With this inclusion, the
@Code "@Graph" symbol used below will then be available for use anywhere
within your document.
@PP
@Code "@Graph" distinguishes between the overall graph, produced by the
@Code "@Graph" symbol itself, and the data sets to be placed within it,
each of which is enclosed by a @Code "@Data" symbol:
@ID @OneRow @Code {
"@CentredDisplay @Graph"
"{"
"    @Data  points { plus }"
"    { 1 1.10  2 1.21  3 1.33  4 1.46  5 1.61  6 1.77  7 1.95  8 2.14 }"
""
"    @Data  points { circle }"
"    { 1 1.20  2 1.44  3 1.73  4 2.07  5 2.45  6 2.99  7 3.58  8 4.30 }"
"}"
}
Although it is good practice to lay the input data out neatly, layout
has no effect on the result.  It is not necessary to have one data point
per line, for example.  The result of this example is
@CentredDisplay @Graph
{
    @Data
        points { plus }
    { 1 1.10  2 1.21  3 1.33  4 1.46  5 1.61  6 1.77  7 1.95  8 2.14 }

    @Data
        points { circle }
    { 1 1.20  2 1.44  3 1.73  4 2.07  5 2.45  6 2.99  7 3.58  8 4.30 }
}
We have used the @Code "@CentredDisplay" symbol from Section
{@NumberOf displays} to produce a centred display, but the
@Code "@Graph" symbol produces an object which may appear anywhere
at all -- in a figure, for example, or as an entry in a table.
@End @Section
