A command-line driven interactive plotting program

 Gnuplot is a portable command-line driven interactive data and function
 plotting utility that supports lots of output formats, including drivers
 for many printers, (La)TeX, (x)fig, Postscript, and so on. The X11-output
 is packaged in gnuplot-x11.
 .
 Data files and self-defined functions can be manipulated by the internal
 C-like language. Can perform smoothing, spline-fitting, or nonlinear fits,
 and can work with complex numbers.
 .
 This package contains the terminal driver that enables gnuplot to plot
 images interactively under X11. Most users will want this, it is however
 packaged separately so that low-end systems don't need X installed to use
 gnuplot.