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# 6. Graphics

Among the scores of graphic packages available, `gnuplot` stands out for its power and ease of use. Go to X and type `gnuplot`, and have two sample data files ready: `2D-data.dat` (two data per line), and `3D-data.dat` (three data per line).

Examples of 2-D graphs:

    gnuplot> set title "my first graph"
    gnuplot> plot '2D-data.dat'
    gnuplot> plot '2D-data.dat' with linespoints
    gnuplot> plot '2D-data.dat', sin(x)
    gnuplot> plot [-5:10] '2D-data.dat'

Example of 3-D graphs (each `row' of X values is followed by a blank line):

    gnuplot> set parametric ; set hidden3d ; set contour
    gnuplot> splot '3D-data.dat' using 1:2:3 with linespoints

A single-column datafile (e.g., a time series) can also be plotted as a 2-D graph:

    gnuplot> plot [-5:15] '2D-data-1col.dat' with linespoints

or as a 3-D graph (blank lines in the datafile, as above):

    gnuplot> set noparametric ; set hidden3d
    gnuplot> splot '3D-data-1col.dat' using 1 with linespoints

To print a graph: if the command to print on your Postscript printer is `lpr -Pps file.ps`, issue:

    gnuplot> set term post
    gnuplot> set out '| lpr -Pps'
    gnuplot> replot

then type `set term x11` to restore. Don't get confused---the last print will come out only when you quit `gnuplot`.

For more info, type `help` or see the examples in directory `/usr/lib/gnuplot/demos/`, if you have it.

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